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Fertility Factors:

Being a healthy weight increases your chances of having a baby. If men or women are overweight, or underweight it can take longer to conceive.

Why? Because it can cause problems with hormone levels, which can affect a woman’s menstrual cycle and the quality of her eggs.

Being overweight can also reduce the quality of a man’s sperm and cause erection problems. It can also affect men's and women's libido (sex drive).

It's not about having some kind of ‘perfect’ body – just a healthy body, because healthier parents have healthier babies.


A man's weight doesn't affect a couple's ability to have a baby.



Men who are overweight or obese have worse sperm quality and are not as fertile as men who are a healthy weight.

  • How can I tell if I’m a healthy weight?

    One way to measure whether you're in a healthy weight range is using the Body Mass Index or BMI. You can enter your height and weight into this BMI calculator to find out your BMI number.

            A BMI between 18.5 and 24.9 is considered a ‘healthy weight’.

            A BMI below 18.5 is considered ‘underweight’.

            A BMI between 25 and 29.9 is considered ‘overweight’.

            A BMI over 30 is considered ‘obese’.


    You can also measure your waist to indicate whether you have a healthy weight.

  • The facts about weight and fertility

    Most of us carry more weight than our parents and grandparents did when they were our age.

    In 2014-15, nearly two-thirds (63 percent) of Australian adults were overweight or obese, and obesity is on the rise. 

    A healthy diet and regular exercise improve your health and your chance of pregnancy and having a healthy baby.

    While studies show that exercise boosts female fertility it is important to note that a large amount of very high intensity exercise may actually reduce fertility and the chance of having a baby with ART. So, it’s a good idea to avoid very high intensity exercise while trying for a baby.

  • Weight and men's fertility

    Overweight and obese men have worse sperm quality than men who are a healthy weight. Being underweight can also reduce a man’s sperm quality and therefore his fertility.

    Being overweight or obese can cause hormonal changes that reduce fertility and make men less interested in sex. Men who are very overweight are also more likely to have problems getting and keeping an erection. Together, these factors reduce the chances of fathering a child.

  • Weight, women's fertility and pregnancy health

    Being a healthy weight increases the chances of getting pregnant and reduces the risk of complications during pregnancy.

    Women who are obese take longer to get pregnant and have a higher risk of:

    •  miscarriage
    •  hypertension (high blood pressure)
    • pre-eclampsia
    • gestational diabetes
    • infection
    • blood clotting
    • the need for medical intervention to bring on labour (induced labour)
    • caesarean birth
    • premature birth
    • stillbirth


    Babies born to women who are obese are more likely than babies born to mothers in the healthy weight range to:

    • be larger than normal at birth
    • need intensive care after birth
    • have a birth defect
    • become obese and have health problems in childhood and later in life.
  • What you can do

    The good news is that by making some changes – eating healthy meals and doing some regular exercise, you can work towards a healthier weight to improve your chance of pregnancy and having a healthy baby.

    If you or your partner are overweight or obese, losing even a few kilos can improve your chances of getting pregnant.

    Losing weight is not easy, and it takes commitment and time. But for most people, it is possible. Research shows that if partners get healthier together, there’s a better chance of success. Having support from a partner, family or friend can help you set up healthy lifestyle habits for the future.

    Men who start healthy eating and exercise more often can increase the quality of their sperm. See How to get ready to be a dad and Your Sperm and how to look after them.

  • Ways to make healthier changes
    • Avoid short-term fad diets or changes that you are unlikely to continue in the future.
    • Set small achievable goals that you can manage (e.g. taking the stairs rather than the lift, using a pedometer to count your steps each day, swapping juice or soft drinks for water).
    • Be realistic and build your goals up slowly over time.
    • Everyone is different. Find a way that works best for you, and fits into your lifestyle.


    Our healthy weight fact sheet and the LiveLighter website offer tips for getting healthier.

    The Dietitians  Association of Australia can help you create your personal healthy eating plan.

    The Australian Government’s Healthy Weight website has information about a balanced diet and explains how much exercise you need to reach and keep a healthy weight.

    The Queensland Government's initiative Healthier. Happieroffers great tips, tools and resources to assist people in making healthy lifestyle changes.

  • Some medical conditions can affect your weight

  • Polycystic ovary syndrome (PCOS)

    In women, unhealthy weight can be associated with a medical condition called polycystic ovary syndrome (PCOS), a common cause of infertility. PCOS is a hormonal condition that affects up to 1 in 7 women of reproductive age. Early diagnosis, a healthy lifestyle and medication can improve fertility for women with PCOS. Find out more about PCOS here.

  • Diabetes

    Diabetes in both men and women affects the chances of having a baby but it can be controlled to reduce or remove symptoms. It is especially important for both men and women with diabetes have a health check to review your diabetes and general health, at least three to six months before trying to have a baby.

    For more information about how to manage diabetes before and during pregnancy visit the National Diabetes Services Scheme (NDSS) Pregnancy & Diabetes website (for women) and Andrology Australia website (for men).

    Find out more about diabetes here.

  • References
    • Adane, A. A., et al. (2018). Maternal preconception weight trajectories are associated with offsprings' childhood obesity. International Journal of Obesity, 24(10), 018-0078.
    • Athukorala, et al. (2010). The risk of adverse pregnancy outcomes in women who are overweight or obese. BMC Pregnancy and Childbirth, 10, 56.
    • Bakos, et al. (2011). Paternal body mass index is associated with decreased blastocyst development and reduced live birth rates following assisted reproductive technology. Fertility and Sterility, 95(5), 1700-1704.
    • Best, D., Avenell, A., & Bhattacharya, S. (2017). How effective are weight-loss interventions for improving fertility in women and men who are overweight or obese? A systematic review and meta-analysis of the evidence. Human Reproduction Update, 23(6), 681-705. doi: 10.1093/humupd/dmx027.
    • Brewer, C. J., & Balen, A. H. (2010). The adverse effects of obesity on conception and implantation. Reproduction, 140(3), 347-364. doi: 10.1530/rep-09-0568.
    • Campbell, J. M., et al. (2015). Paternal obesity negatively affects male fertility and assisted reproduction outcomes: a systematic review and meta-analysis. Reproductive Biomedicine Online, 31(5), 593-604.
    • Cheney, K., et al. (2018). Population attributable fractions of perinatal outcomes for nulliparous women associated with overweight and obesity, 1990–2014. Medical Journal of Australia, 208(3), 119-125.
    • Cleo, G., et al. (2018). Habit-based interventions for weight loss maintenance in adults with overweight and obesity: a randomized controlled trial. International Journal of Obesity. doi: 10.1038/s41366-018-0067-4.
    • Craig, J. R., et al. (2017). Obesity, male infertility, and the sperm epigenome. Fertility and Sterility, 107(4), 848-859. doi:
    • Dodd, et al. (2011). Maternal and perinatal health outcomes by body mass index category. Australian and New Zealand Journal of Obstetrics and Gynaecology, 51, 136-140.
    • Fullston, T., et al., The most common vices of men can damage fertility and the health of the next generation. Journal of Endocrinology, 2017. 234(2): p. F1-F6.
    • Gaskins, A. J. (2018). Moving the science forward on dietary patterns and male fertility. Fertility and Sterility. doi:
    • Gesink Law, et al. (2007). Obesity and time to pregnancy. Human Reproduction, 22(2), 414-420.
    • Harrison, C. L., et al. (2017). Preventing obesity across the preconception, pregnancy and postpartum cycle: Implementing research into practice. Midwifery, 52, 64-70. doi:
    • Homan, G. F., Davies, M. J., & Norman, R. J. (2007). The impact of lifestyle factors on reproductive performance in the general population and those undergoing infertility treatment: a review. Human Reproduction Update, 13(3), 209-223.
    • Jackson, et al. (2015). The influence of partner’s behavior on health behavior change: The English longitudinal study of ageing. JAMA Internal Medicine, 175(3), 385-392. doi: 10.1001/jamainternmed.2014.7554.
    • Lan, L., et al. (2017). Systematic review and meta-analysis of the impact of preconception lifestyle interventions on fertility, obstetric, fetal, anthropometric and metabolic outcomes in men and women. Human Reproduction.
    • Luke, B., et al. (2011). Female obesity adversely affects assisted reproductive technology (ART) pregnancy and live birth rates. Human Reproduction, 26(1), 245-252.
    • MacDonald, et al. (2013). Body mass index in relation to semen quality and reproductive hormones in New Zealand men: a cross-sectional study in fertility clinics. Human Reproduction, 28(12), 3178-3187. doi: 10.1093/humrep/det379.
    • Marchi, J., et al. (2015). Risks associated with obesity in pregnancy, for the mother and baby: a systematic review of reviews. Obesity Reviews, 16, 621-638. doi: 10.1111/obr.12288.
    • Mutsaerts, M. A. Q., et al. (2014). Effects of paternal and maternal lifestyle factors on pregnancy complications and perinatal outcome. A population-based birth-cohort study: the GECKO Drenthe cohort. Human Reproduction, 29(4), 824-834. doi: 10.1093/humrep/deu006.
    • Petersen, et al. (2013). The influence of female and male body mass index on live births after assisted reproductive technology treatment: a nationwide register-based cohort study. Fertility and Sterility, 99(6), 1654-1662. doi: 10.1016/j.fertnstert.2013.01.092.
    • Practice Committee of the American Society for Reproductive, M. (2015). Obesity and reproduction: a committee opinion. Fertility and Sterility, 104(5), 1116-1126. doi:
    • Salas-Huetos, A., et al. (2017). Dietary patterns, foods and nutrients in male fertility parameters and fecundability: a systematic review of observational studies. Human Reproduction Update, 23(4), 371-389. doi: 10.1093/humupd/dmx006.
    • Salas-Huetos, A., et al., Male adiposity, sperm parameters and reproductive hormones: An updated systematic review and collaborative meta-analysis. Obesity Reviews, 2020. 
    • Sharma, R., et al. (2013). Lifestyle factors and reproductive health: taking control of your fertility. [Review]. Reprod Biol Endocrinol, 11(66), 1477-7827.
    • Stephenson J, Heslehurst N, Hall J, Schoenaker DAJM, Hutchinson J, Cade JE, Poston L, Barrett G, Crozier SR, Barker M et al. Before the beginning: nutrition and lifestyle in the preconception period and its importance for future health. The Lancet 2018;10.1016/S0140-6736(18)30311-8.
    • Wright, S., & Aronne, L. (2012). Causes of obesity. Abdominal Imaging, 37(5), 730-732. doi: 10.1007/s00261-012-9862-x.

Page created on: 29/08/2018 | Last updated: 24/01/2022

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