Trouble-Shooting Fertility!

Hello and welcome to my blog!

If you or your partner have struggled to conceive, you’re not alone. About 25% of couples in the United States struggle with subfertility or infertility (Mol, 2018). For 12-15% of those couples, fertility issues occur without a diagnosable cause and can leave couples frustrated and wondering what to do. Fertility treatments and IVF can be expensive and are rarely covered by insurance. One couple I worked with was preparing for their 21st IVF procedure when they came to my office (that’s so many!). They had heard through the grapevine that chiropractic was a great way to keep your body in optimal health and they were hoping chiropractic would help them finally conceive. I explained that proper coordination and expression of the nervous system was imperative for a successful ovulation, but that it seemed these two needed more than just an adjustment. We stopped and discussed several things about their lifestyle that needed correcting before they proceed. Today, I wanted to share with you seven common causes of subfertility or infertility. I use the term “subfertile” as well as “infertile” because most women are failing to properly ovulate but can still become pregnant and maintain a healthy pregnancy when their needs are properly addressed. One in seven couples who struggle with infertility are actually subfertile (Thurston, 2018). Other women may have underlying conditions that make it extremely unlikely or impossible for them to get or keep a pregnancy. There are many reasons why both men and women would have a difficult time conceiving.

Infertility is defined when there is a failure to conceive after 12 consecutive months of trying (Mol, 2018). Symptoms of infertility for women include PCOS, absent or irregular menstruation, loss or thinning of the hair, excessive facial hair, or sudden changes in weight. Signs of infertility in men include lack of facial hair growth, change in sexual appetite, erectile disfunction (ED), or painful, small or firm testicles. If this describes you, then it is important to see a fertility specialist and identify why you or your partner are failing to conceive. Many fertility treatments have side effects and can be costly. Once your doctor has identified the cause of infertility, it can be properly treated. For those who have no idea why they are not getting pregnant or can’t afford to see a specialist, here are a few suggestions to optimize your body’s chance of getting and maintaining a healthy pregnancy. 

Dehydration

How much water do you drink a day? I frequently check in with my patients about their water intake and this isn’t because I like making my patient feel bad about not drinking enough water, but because it is imperative for almost all the cellular activity in your body. 50-80% of your body weight is water; blood is 85% water, muscles are 80% water, your brain ranges from 75-90% water and even your bones are 25% water (Chang, 2020). When your body needs water, it looks to steal it from the reproductive system first since you do not need this system to live. For men, dehydration can lead to decreased sperm motility, quality, and volume (Chang, 2020). For women, dehydration results in poor egg health, damaged eggs, and decreased cervical mucus secretion which is needed for transportation of sperm to the fallopian tubes (Chang, 2020). Dehydration doesn’t only affect fertility, but also affects the ability to maintain a healthy pregnancy. During pregnancy, blood volume increases and hormones need to be transported to different parts of the body (Pinto, 2022). Harmful toxins must be flushed out and eliminated while nutrients must be carried to the baby. Water is the primary mover and facilitator of all these processes! How is your body supposed to coordinate all of this without enough water? In addition to the harm dehydration does to your body, becoming dehydrated can cause mood dysregulation, disrupting the mind-body connection, which is important for maintaining your fertility (Pinto, 2022). Fact is, you need water to function, but you especially need it if you want to have or maintain a healthy pregnancy. 

Now that you know water is important and you should drink it, let's talk about how to properly drink water (because you're probably doing it wrong!). First, the general rule of thumb is you need half your body weight in oz. per day for basic functioning. So if you are already dehydrated, add 30-40 oz to that to begin catching up. Second, when trying to hydrate you should sip water, not chug it. When you chug water, your body will only absorb about 30-40% of it. When you sip your water, your body has time to absorb it properly. Third, when drinking caffeinated beverages, forget about double fisting with a water bottle because you won’t be able to absorb water for a few hours now. I used to be that person who would chug a bottle of water with my coffee to stay hydrated, however caffeine is a diuretic and will remain in your system for several hours after consumption. You can’t absorb water and drink diuretics at the same time! When I am trying to hydrate, I start my morning off with 32 oz of water and I wait until the late morning or early afternoon to have a cup of coffee (I’m a coffee addict and have to have at least one cup!). I wait a few hours and switch to water for the rest of the day. Lastly, water follows salt. It is important to have some amount of sugars or salts so that you can absorb the water you drink. Patient’s often tell me they have cut sugar and salt from their diet and now they are always dehydrated despite drinking plenty of water. That is probably a sign your solute concentration is off. I personally use a product called Dripdrop ORS which has the same tested effectiveness as an IV at the hospital. This product is also safe for pregnant women and women who are lactating and has ⅓ of the sugar as other electrolyte mixes! Plus it tastes pretty good.  

When drinking water, it is imperative you avoid plastic (especially BPA materials). Even BPA-free water bottles release estrogen mimicking chemicals that affect hormone regulation. Heating plastic containers and water bottles releases these chemicals 55 times faster than normal (U.S. Department of Health and Human Services, 2022). My favorite water bottle in grad school was a good old fashioned mason jar! I now use a water bottle with time measurements on it to help me stay motivated to drink water throughout the day. I also recommend finding an app to track your water intake such as Aqualert, Waterlogged, or Plant Nanny (This one lets you water plants in a video game-like app when you log your own water intake!). Drinking water isn’t just for those who want to get pregnant, but for anyone who wants to give their body a boost in function! 

Stress

According to the National Institute of Health, stress is the major contributing factor for the six leading causes of death in the United States; cancer, heart disease, accidental injuries, respiratory disorders, cirrhosis of the liver and suicide (Salleh, 2008). Stress has also been found to contribute to infertility issues in both men and women. Women who reported high levels of stress were twice as likely to have infertility issues while men showed decreased sperm count and motility (C.D. Lynch, 2014). Women who tested for high levels of alpha-amylase (a marker that also indicates too much cortisol in the body), were 29% less likely to become pregnant each month. But why is stress so harmful for people trying to conceive? Well, when your body has to make cortisol (stress hormone) it has to stop making other hormones which offsets the balance of estrogen and progesterone, FSH, Luteinizing hormone, etc. It even lowers testosterone in men which affects sperm development, maturity, and health. Stress has also been associated with erectile dysfunction, especially because stressing about ED causes more ED! How does stress contribute to some ED cases? Chronic stress and anxiety can affect your brain’s ability to signal your body’s physical response, and interrupt how your brain sends messages to allow extra blood flow to erectile tissue (Holland, 2017). 

When discussing stress with my patients wo are trying to conceive, I am not suprised to find that many couples have had issues with miscarriages, and that they often coincided with a stressful event or time in their life. I inform my patients about the early stages of pregnancy, and that the placenta doesn’t implant until the 12th-15th week depending. Why is this important? When someone is pregnant and stressed, their body has to stop making hormones to support the pregnancy and instead makes cortisol. The placenta can create and maintain all the hormones needed to properly support a growing fetus, but until that happens, you’re on your own momma. Minimizing stress during the early stages of pregnancy can help reduce the risk of miscarriage. A systematic review and meta-analysis found that psychological stress can increase the risk of miscarriage by as much as 42% (Qu, 2017)! The study also indicated that eliminating stressors before trying to become pregnant might shorten the time couples need to become pregnant in comparison to ignoring stress. It’s important to find a stress reduction technique that works for you and can include yoga, deep breathing, therapy, meditation and mindfulness. 

Now, I can’t talk about stress without talking about fear of pregnancy, birth and motherhood. I have worked with a few clients who had a serious mental block when it came to getting pregnant. They often had an unexpressed concern that they needed to address before getting pregnant. For some, it involved talking about fears for their relationship after having a baby, financial stressors, lack of support systems, fear of birth, motherhood, or working together as parents. It is always helpful to seek couples counseling if there are any concerns you or your partner have about bringing a new human into the world. It can be a big and scary decision, but knowledge is power. Ask questions, seek answers, express your wants, needs expectations and concerns. Your partner should be willing to listen and problem solve with you as you both need to feel loved and supported through this process! 

Poor Diet

Diets high in unsaturated fats, whole grains, vegetables, and fish have been associated with improved fertility in both women and men (Panth, 2018). While current evidence on the role of dairy, alcohol, and caffeine is inconsistent, saturated fats, and sugar have been associated with poorer fertility outcomes in women and men (Chavarro, 2007). Furthermore, U.S. women who belong to an underrepresented minority group, have low income, or have a low level of education, have significantly higher rates of infertility outcomes as compared to women who are white, have high income, or have high educational attainment (Chavarro, 2007). Healthy food can be expensive and knowing what to eat can be tricky (especially if you don’t know how to read food labels). Access to fresh fruits and vegetables can be difficult, especially in “food deserts'' seen within cities like Reading or Philadelphia or if a person needs to rely on public transport to reach food. It is important to have a variety of fresh produce when trying to conceive so that you can get as many vitamins and minerals from food as possible. Prenatals and other vitamins are great, but getting nutrients directly from the source is how our body works best! 

In a Nurses' Health Study (NHS), women who had the highest intake of a “fertility diet” comprised of proteins mostly from plants, full-fat dairy foods, iron, and healthy monounsaturated fats, were found to have a 66% lower risk of infertility related to ovulatory disorders and a 27% lower risk of infertility due to other causes (Westphal, 2006). A healthy diet isn’t just good for conceiving, but also good for mental health, gut health, and heart health! When a patient isn’t able to adequately change their diet to better support pregnancy, I recommend supplements depending on the individual and their needs. Adding extra folate supplements can also reduce the risk of spontaneous abortion, but only when consuming greater than 730 μg per day. (Gaskins, 2014).  Iron supplements can significantly lower risk of ovulatory infertility than women who did not use iron supplements (Chavarro, 2006).

Some studies suggest avoiding certain foods as well. Each individual is different and can be affected by food differently. For example, my body does not do well without red meat on occasion. I have attempted to be a vegetarian on different occasions and have been hospitalized both times for severe malnutrition and anemia. However, other women may feel more energy, have better weight control, and less chronic pain when cutting out red meat. The consumption of red meat has been shown to have a negative effect on blastocyst formation during the early stages of pregnancy. The likelihood of blastocyst formation was also negatively influenced by the consumption of alcohol and cigarettes (Braga, 2015). Foods or beverages high in sugar are also best to avoid according to a cohort study of 3,628 women planning to become pregnant. The women who reported consuming 3 or more servings of soda per day had a 52% lower rate of pregnancy compared to women who did not report any soda consumption (Hatch, 2012)! This same study found no association between coffee consumption and fertility issues (thank goodness because I love coffee too much to give it up!). 

Unhealthy Weight

I don’t often talk about weight with a patient unless they request to do so, or if we need to discuss posture and how they carry their body (it’s how you carry your weight that matters more than what you weigh!). When discussing concerns about getting pregnant, I have had a few patients who needed to lose or gain weight for their body to undergo IVF treatments or to get and maintain a healthy pregnancy. Studies show that the risk of infertility is highest among those at the lowest and highest ends of the BMI scale (Chavarro, 2007). If your body does not have enough fat storage to promote proper hormone production or to maintain a pregnancy, this can make getting pregnant difficult. People who are underweight can also have issues with irregular periods and can sometimes stop having a period altogether. While I was playing rugby in college, I would go the whole season without getting a period due to the amount of fat I was burning and my body no longer had enough energy to support a pregnancy. My body felt that there was no longer a reason to ovulate if I couldn’t support an infant. For individuals who are underweight and do become pregnant, they run the risk of “miscarriage, premature birth, stillbirth and delivering low birth weight babies at a much higher rate than their healthier peers” (LA IVF, 2022). 

 Women who have a high BMI and have insulin resistance also have an increased risk of gestational diabetes and preeclampsia which can cause significant risks to the mother and baby. Body fat plays a role in the function of the endocrine system, and imbalances in this system can cause irregular ovulation. This isn’t only true for women, but for men as well. Men who are overweight have an increased risk of infertility, potentially through endocrine dysregulation mechanisms (Hammoud, 2008). Men who are underweight may suffer from low testosterone levels which can impact sperm quality, libido and contribute to ED (LA IVF, 2022). I often encourage couples to start making dinner together, going for walks, and working with a nutritionist to help them reach their healthy weight goals. I also recommend talking with a therapist if you struggle with an eating disorder and would like to get pregnant. Having some extra support while your body undergoes changes in weight and shape during pregnancy can also be beneficial for your mental health and wellbeing while pregnant. 

Hormone Disruption 

So far we have already touched on several topics that affect hormone pathways in the body: dehydration, stress, diet, and weight. If you are struggling to get pregnant, then you should also consider getting your hormones tested to know where your body is at and how to better support your endocrine function. Many women who seek fertility treatments are told that they are not ovulating properly. When I ask my patient if they know why they are not ovulating properly they often have no idea and no one has explained this yet. I tell them how proper support of their endocrine system is important for successful ovulation. In fact, successful ovulation induction in anovulatory women is possible for nearly all women except in cases of ovarian failure (Adamson, 2003). Knowing why your hormones are dysregulated will allow you to take steps to support your endocrine system and improve your chances of getting pregnant and your overall health.

For example, hormones can be disrupted by nutritional deficiencies such as vitamin A (eat more cooked carrots!). Vitamin A is essential for normal male reproduction and helps with sperm quality and motility (Adamson, 2003). Having a history of cancer or cancer treatments can also affect your hormone function. Testicular or prostate cancer as well as ovarian, uterine or breast cancer can change the physiology and function of the reproductive system. Chemotherapeutic agents and radiation also increase the risk of infertility by causing disruption of hormone pathways. Undiagnosed thyroid disorders such as hypo or hyperthyroid can also affect sperm production in men and ovulation in women. Determining the presence of automimmune thyroid conditions like Hashimoto’s can be useful in identifying women at risk for miscarriage as well (Poppe, 2002). Other reproductive conditions like PCOS are known for their hormone dysregulation, which is characterized by high androgen levels, disruption of ovarian folliculogenesis, and even outward masculine appearance such as a mustache and beard formation (Adamson, 2003). 

One of the biggest disruptors of hormones in the body are chemicals known today as endocrine-disrupting chemicals. These EDCs affect egg production (oogenesis) in females and can affect sperm formation and maturation. Exposure to such compounds can lead to permanent infertility in females due to the finite number of eggs women are born with. As previously mentioned, avoiding plastic containers for food and beverages can help lower your exposure to these chemicals. I also avoid chemicals such as DEET (Segal, 2017) found in bug sprays and glyphosate (found in RoundUp Weed Killer) as these two chemicals are suspected to increase infertility risk (Samsel, 2013). Switching to all natural cleaning products is another way to decrease your exposure to such chemicals as well as avoiding clothing or fabrics with fire retardants. A growing body of evidence shows that fire retardants have adverse health effects, “including endocrine and thyroid disruption, impacts to the immune system, reproductive toxicity, cancer, and adverse effects on fetal and child development and neurologic function” (Shaw, 2010). It’s important to remember that your skin is a giant sensory organ that also absorbs chemicals that it comes in contact with!

Smoking

Smoking can also affect your endocrine system, but it also affects every other system in your body! When you smoke, not only are you introducing harmful chemicals to your body, but you are also decreasing oxygen to every cell in your body! Studies performed on women who are receiving IVF treatments showed that smoking during the treatment cycle resulted in a “50% reduction in implantation rate and ongoing pregnancy rate compared with women who had never smoked” (Van Voorhis, 1996). This study also found that smoking seems to have a temporary toxic effect on fertility, because current smokers, but not past smokers, had a reduced pregnancy rate after compared with nonsmokers. I suggest quitting smoking while you're ahead! Another study found that six or more cigarettes smoked per day was all it took to significantly lower fertility (Sarokhani, 2017). This does not mean that smoking only a few cigarettes a day is harmless, but that smoking six cigarettes is the same as smoking a whole pack when it comes to fertility issues. 

Smoking has shown to directly affect reproductive organ function by causing blockages in the fallopian tubes, which prevents the egg and sperm from meeting and results in an increased risk of ectopic pregnancy (Practice Committee of the American Society for Reproductive Medicine, 2012). Smoking also damages eggs while they are maturing in the ovaries which also doesn’t only affect the eggs ability to become fertalized, but also can increase the risk of miscarriage. Women also have a finite number of eggs and once they are damaged, there is no going back. The fascinating field of epigenetics has shown that if your grandmother smoked while pregnant, then your eggs have already been damaged by smoking! Smoking also can lead to a women entering menopause up to four years early, so if you are a smoker and waiting until you’re in you late 30’s or early 40’s to have children, you might be too late. Smoking also affects the quality of the uterine lining, which may prevent proper embryo implantation. These changes to the cervical and uterine mucus are also associated with cervical cancer (Sugawara, 2019). It’s never too late to quit smoking. If you or your partner would like more information on smoking cessation, I suggest talking with your doctor or visiting https://www.quit.com. 

Lack of Sleep/Night Shift

When it comes to feeling good, whether menatally, physically, or emotionally, sleep is imperative. When your schedule doesn’t allow for enough sleep, your mind, body and spirit suffer.  It is recommended that if you and your partner are trying to conceive, you should avoid the night shift, if possible. Your sleep pattern or circadian rhythm can alter many physiological systems, including your immune system, endocrine system, and reproduction. Conditions like endometriosis and menstrual irregularity are common among night shift workers. Regularly working the night shift negatively affects hormone production and affects the quality of egg and sperm production (who would have guessed?). In a prospective study of couples attending a fertility center, women who worked evenings, nights, or who worked rotating shifts had significantly lower oocyte yield compared to day workers (Fernandez, 2020). It’s not just when you are able to go to sleep that matters, but the quality of sleep as well. A good night's sleep should be uninterrupted, deep and restful. It’s also important to limit your amount of screen time before bed and sleep in complete darkness. Some studies indicate that sleeping with the TV or other lights on affects your body’s ability to enter a deep sleep and can negatively affect your circadian rhythm by altering melatonin production and overstimulating the brain. It is important to try to wake up at a consistent time in the morning as well to help regulate your body’s natural circadian rhythm. 

 If you do work the night shift, try to get enough sleep when you're not working by creating a sleep schedule, allowing times for naps, and not using stimulants to push you through the day. Your body needs sleep in order to heal and function appropriately so if you are tired, you need to find some time for shut eye. If you are undergoing IVF, the American Society for Reproductive Medicine recommends getting at least 7-8 hours of sleep enough to successfully ovulate.

 In a previous blog post I discussed how I adjust the sphenoid for patients who have endocrine dysfunction or circadian rhythm disruption to help improve the quality of sleep and regulate hormone production. If you have insomnia, sleep apnea, or other sleep disorder it is important to get treated so your body can get the rest it needs.

When attempting to conceive it is important for you and your partner to seek every advantage in the game of life. Sleep well, eat well, drink water, and stress less. A healthy baby starts with healthy parents. If you smoke or drink heavily I suggest cutting back or quitting while trying to get pregnant. If you have been having issues for the last year with getting or maintaining a pregnancy, meet with a fertility specialist, ask your family doctor for bloodwork or hormone testing, and see your chiropractor to improve the function of your neuro-muscular-skeletal system! 

Feel well and do good,

ADIO

Dr. Tabetha Super

References

1. Mol BW, Tjon-Kon-Fat R, Kamphuis E, van Wely M. Unexplained infertility: Is it over-diagnosed and over-treated? Best Pract Res Clin Obstet Gynaecol. 2018 Nov;53:20-29. doi: 10.1016/j.bpobgyn.2018.09.006. Epub 2018 Oct 6. PMID: 30518485.

2. Thurston L, Abbara A, Dhillo WS. Investigation and management of subfertility. J Clin Pathol. 2019 Sep;72(9):579-587. doi: 10.1136/jclinpath-2018-205579. Epub 2019 Jul 11. PMID: 31296604.

3. Chang, J. (2020, June 2). Can drinking water improve your fertility? Fertility Road Magazine. Retrieved May 16, 2022, from https://fertilityroad.com/can-drinking-water-improve-your-fertility/ 

4. Pinto, A. (n.d.). How hydration affects fertility. Repromed Fertility center. Retrieved May 16, 2022, from https://www.repromedfertility.com/blog/how-hydration-affects-fertility-4153/ 

5. U.S. Department of Health and Human Services. (n.d.). Endocrine disruptors. National Institute of Environmental Health Sciences. Retrieved May 16, 2022, from https://www.niehs.nih.gov/health/topics/agents/endocrine/index.cfm 

6. Salleh M. R. (2008). Life event, stress and illness. The Malaysian journal of medical sciences : MJMS, 15(4), 9–18.

7. C.D. Lynch, R. Sundaram, J.M. Maisog, A.M. Sweeney, G.M. Buck Louis, Preconception stress increases the risk of infertility: results from a couple-based prospective cohort study—the LIFE study, Human Reproduction, Volume 29, Issue 5, May 2014, Pages 1067–1075, https://doi.org/10.1093/humrep/deu032

8. Holland, K. (2017, July 1). Can stress and anxiety cause erectile dysfunction? Healthline. Retrieved May 22, 2022, from https://www.healthline.com/health/erectile-dysfunction-anxiety-stress#causes 

9. Qu F, Wu Y, Zhu Y et al. The association between psychological stress and miscarriage: A systematic review and meta-analysis. Sci Rep. 2017;7(1). doi:10.1038/s41598-017-01792-3

10. Panth, N., Gavarkovs, A., Tamez, M., & Mattei, J. (2018). The Influence of Diet on Fertility and the Implications for Public Health Nutrition in the United States. Frontiers in public health, 6, 211. https://doi.org/10.3389/fpubh.2018.00211

11. Chavarro JE, Rich-Edwards JW, Rosner BA, Willett WC. Diet and lifestyle in the prevention of ovulatory disorder infertility. Obstet Gynecol. (2007) 110:1050–8. 10.1097/01.AOG.0000287293.25465.e1

12. Westphal LM, Polan ML, Trant AS. Double-blind, placebo-controlled study of Fertilityblend: a nutritional supplement for improving fertility in women. Clin Exp Obstet Gynecol. (2006) 33(4):205–8.

13. Gaskins AJ, Rich-Edwards JW, Hauser R, Williams PL, Gillman MW, Ginsburg ES, et al. . Maternal prepregnancy folate intake and risk of spontaneous abortion and stillbirth. Obstet Gynecol. (2014) 124:23–31. 10.1097/AOG.0000000000000343 

14. Chavarro, Jorge E. MD, ScD; Rich-Edwards, Janet W. MPH, ScD; Rosner, Bernard A. PhD; Willett, Walter C. MD, DrPH Iron Intake and Risk of Ovulatory Infertility, Obstetrics & Gynecology: November 2006 - Volume 108 - Issue 5 - p 1145-1152 doi: 10.1097/01.AOG.0000238333.37423.ab

15. Braga, Daniela Paes Almeida Ferreira, Gabriela Halpern, Amanda S. Setti, Rita Cássia S. Figueira, Assumpto Iaconelli, Edson Borges, “The impact of food intake and social habits on embryo quality and the likelihood of blastocyst formation”, Reproductive BioMedicine Online, Volume 31, Issue 1, 2015, Pages 30-38, ISSN 1472-6483, https://doi.org/10.1016/j.rbmo.2015.03.007. (https://www.sciencedirect.com/science/article/pii/S1472648315001480)

16. Hatch EE, Wise LA, Mikkelsen EM, Christensen T, Riis AH, Sorensen HT, et al. . Caffeinated beverage and soda consumption and time to pregnancy. Epidemiology (2012) 23:393–401. 10.1097/EDE.0b013e31824cbaac 

17. Hammoud AO, Gibson M, Peterson CM, Meikle AW, Carrell DT. Impact of male obesity on infertility: a critical review of the current literature. Fertil Steril. (2008) 90:897–904. 10.1016/j.fertnstert.2008.08.026

18. Adamson GD, Baker VL. Subfertility: causes, treatment and outcome. Best Pract Res Clin Obstet Gynaecol. 2003 Apr;17(2):169-85. doi: 10.1016/s1521-6934(02)00146-3. PMID: 12758094.

19. Poppe K, Velkeniers B. Thyroid and infertility. Verh K Acad Geneeskd Belg. 2002;64(6):389-99; discussion 400-2. PMID: 12649931.

20. Segal, T. R., Mínguez-Alarcón, L., Chiu, Y. H., Williams, P. L., Nassan, F. L., Dadd, R., Ospina, M., Calafat, A. M., Hauser, R., & Earth Study Team (2017). Urinary concentrations of 3-(diethylcarbamoyl)benzoic acid (DCBA), a major metabolite of N,N-diethyl-m-toluamide (DEET) and semen parameters among men attending a fertility center. Human reproduction (Oxford, England), 32(12), 2532–2539. https://doi.org/10.1093/humrep/dex327

21. Samsel A, Seneff S. Glyphosate’s Suppression of Cytochrome P450 Enzymes and Amino Acid Biosynthesis by the Gut Microbiome: Pathways to Modern Diseases. Entropy. 2013; 15(4):1416-1463. https://doi.org/10.3390/e15041416

22. Shaw SD, Blum A, Weber R, Kannan K, Rich D, Lucas D, Koshland CP, Dobraca D, Hanson S, Birnbaum LS. Halogenated flame retardants: do the fire safety benefits justify the risks? Rev Environ Health. 2010 Oct-Dec;25(4):261-305. doi: 10.1515/reveh.2010.25.4.261. PMID: 21268442.

23. Van Voorhis BJ, Dawson JD, Stovall DW, Sparks AE, Syrop CH. The effects of smoking on ovarian function and fertility during assisted reproduction cycles. Obstet Gynecol. 1996 Nov;88(5):785-91. doi: 10.1016/0029-7844(96)00286-4. PMID: 8885914.

24. Practice Committee of the American Society for Reproductive Medicine. Smoking and infertility: a committee opinion. Fertil Steril. 2012;98(6):1400-6. doi:10.1016/j.fertnstert.2012.07.1146

25. Sugawara Y, Tsuji I, Mizoue T, et al. Cigarette smoking and cervical cancer risk: an evaluation based on a systematic review and meta-analysis among Japanese women. Jpn J Clin Oncol. 2019;49(1):77-86. doi:10.1093/jjco/hyy158)

26. Fernandez, R. C., Moore, V. M., Marino, J. L., Whitrow, M. J., & Davies, M. J. (2020). Night Shift Among Women: Is It Associated With Difficulty Conceiving a First Birth?. Frontiers in public health, 8, 595943. https://doi.org/10.3389/fpubh.2020.595943