Lifestyle, BMI And Fertility

3,5 BMI & lifestyle

Midland Fertility helps patients to try to conceive a baby, but patients can help themselves, before and during any treatment, to increase the chances of conception and of having a healthy baby.

Modern life is not very good for fertility; diet, lack of exercise, smoking, alcohol and even some jobs can reduce fertility making it more difficult to conceive.  The following information gives people who are planning – or who are finding it difficult – to conceive, a few ideas about making some changes to their lives, to increase their chances of conceiving either naturally or with assisted conception:

Weight and fertility

There is sound evidence that being significantly over or under-weight can reduce fertility.  In some women, a change of just + or ─ 15% in BMI can change the pattern of their periods and even create fertility problems.  Midland Fertility usually treats women patients with a Body Mass Index (BMI) of 19 to 30.  BMI is calculation of a person’s height to weight ratio.


less than 15 seriously underweight
15 – 19 underweight
19 – 25 normal
25 – 30 overweight
30 – 40 obese
40+ morbidly obese
Go to BMI calculator

Low BMI, conception and pregnancy

Women need body fat in order to have periods.  A very low BMI (ie under 19) may have the following effects on a woman’s fertility and any pregnancy:

  • she will have reduced hormone levels making it more difficult to conceive
  • she may not have regular periods, reducing the chance of conceiving, either naturally or with assisted conception
  • if she does conceive, she has a higher risk of miscarriage and her baby has an increased chance of a lower birth rate
  • if she gives birth, evidence indicates she may experience increased exhaustion and depression when the baby is newborn
  • it may increase complications during fertility treatment and pregnancy and increase the risk of premature delivery and neo-natal death

High BMI, conception and pregnancy

A very high BMI may itself be the cause of a woman’s infertility, or it may complicate other existing causes of infertility and can make fertility treatment more difficult:

  • it can reduce the quality of the uterine lining (the endometrium) and prevent ovulation
  • ultrasound scanning and obtaining accurate clinical measures is difficult because the increase in fatty tissue between the ultrasound probe and the ovaries
  • egg recovery and embryo transfer can be more uncomfortable and risky because fat effects the quality of ultrasound images making it difficult to see the ovaries and retrieve the eggs and increasing the chance of bleeding and bowel puncture
  • higher doses of drugs are often required, so increasing the cost of treatment to privately-funded patients
  • lack of response to treatment or the increased risks of OHSS means an increased chance of cancelling the treatment cycle before embryo transfer
  • following fertility treatment, at least two deaths in the UK have highlighted obesity as a contributing factor

The risks of high BMI during pregnancy

The risks of an increased BMI during pregnancy include mild, but uncomfortable and temporary, ailments, to conditions which are long-term, permanent or life threatening – to the mother and/or baby – including:

  • back pain
  • varicose veins
  • haemorrhoids
  • gestational diabetes
  • high blood pressure or pre-eclampsia
  • increased risk of miscarriage
  • need for premature delivery of the baby
  • difficulty monitoring the pregnancy
  • increased rates of neo-natal death

Midland Fertility has helped many women change their weight before fertility treatment begins to increase the chance of success of the treatment cycle, by:

  • addressing weight issues early
  • advising patients how to adjust their weight – but not by diet alone
  • assessing the realistic opportunities to exercise
  • creating a positive and supportive environment
  • discussing the possible use of alternative therapies, eg hypnotherapy or acupuncture
  • arranging a possible GP referral to a dietician
  • considering the benefits of WeightWatchers® or Slimming World®

Where age is not an issue, weight adjustment may take some months, but it is worth it to increase the chance of a positive pregnancy test, a good pregnancy and a healthy baby, as well as the added non-fertility benefits to the woman’s health.

High BMI and male fertility

In addition to the general health risks of a high BMI, a man with a BMI of 25+ has fewer well-formed, motile sperm per ejaculate, and therefore an increased chance of fertility problems and the need for his partner to possibly undergo ICSI treatment.

What we drink

Few adults drink as much water and juice as is recommended.  But increasing fluid intake to about 6 pints of water or juice (not alcohol, coffee or fizzy drinks!) a day can help general health and well-being and also have a positive impact on fertility.

Some drinks are actually harmful to man or woman’s fertility and if they are having problems conceiving, should be massively reduced or even totally avoided:


There is evidence to suggest that women should avoid alcohol if they are trying to become pregnant because the ability to conceive is lower in couples where the woman drinks alcohol.  Drinking alcohol while pregnant increases the chance of miscarriage and may also cause Fetal Alcohol Syndrome (FAS).  FAS babies have small heads, a flat mid-face, small eyelids and a low nasal ridge and a spectrum of learning and behaviour problems.

Research has also shown that alcohol is toxic to sperm, and so damages a man’s fertility by lowering the sperm count or decreasing sperm motility.

Binges or sudden high levels of alcohol seem to do the most damage for both men and women. Therefore, MFS suggests preferably giving up alcohol whilst trying to conceive, or at least limiting alcohol to recommended maximum daily intakes.

The Department of Health advises that men should not drink more than three to four units of alcohol per day, and women should drink no more than two to three units of alcohol per day.  These daily benchmarks apply whether someone drinks alcohol every day, once or twice a week, or occasionally.  A unit of alcohol is approximately ½ pint of lager or cider, half a glass of wine or a single unit of spirits.


A cup of coffee has twice the amount of caffeine as a single can of cola and much more than a cup of tea.  Studies have shown that caffeine may be related to both an increased risk of miscarriage and a higher risk of developing endometriosis, which can cause painful and heavy periods, make it difficult to conceive and cause early miscarriage.  If giving it up completely is not possible, best advice is to limit caffeine to two cups of coffee a day.


Smoking makes it difficult to conceive, irrespective of whether it is the male or female partner who smokes.  The chance of successful fertility treatment is also reduced.  If a smoker stops, the chance of natural conception increases, as does that of successful fertility treatment.

Nicotine affects the production of hormones necessary for pregnancy and smoking also impedes the transportation of the egg through the Fallopian tubes to the uterus; it is also toxic to sperm.  Even if a couple conceives, they run a greater risk of losing the baby if the mother is a smoker.  Smoking during pregnancy increases the risk of miscarriage, or of the baby dying shortly after birth.

Help to quit smoking is available from GPs or pharmacists.

Non-prescription drugs

Non-prescription and illegal drugs can cause fertility problems, eg:

  • cocaine constricts blood vessels which can result in irregular periods and problems with the placenta during a pregnancy
  • marijuana lowers a man’s sperm count, decreases sperm motility, lowers the amount of testosterone and increases the number of abnormal sperm. In women it increases the number of abnormal eggs
  • anabolic steroids may be used by some men to increase muscle mass, but they also suppress the body’s ability to produce testosterone which is necessary for sperm production

When the heat is on . . .

. . . sperm slow down!  His job may be stopping him being a dad!  Reps, lorry drivers, welders and chefs spend most of their days with ‘hot groins’ from sitting down for prolonged periods or close proximity to a welding torch or oven.  Heat raises the temperature of their testes which is no good for sperm production.  Wearing loose fitting shorts instead of tight underwear may help.

Jobs in manufacturing or construction where men are exposed to lead can diminish male fertility by causing low sperm count and poor sperm motility.  Likewise, exposure to chemicals, radiation or anaesthetics can be harmful to both men’s and women’s fertility and so these types of jobs are worth mentioning when seeing a GP or fertility specialist about having trouble conceiving.

Folic acid

Taking folic acid from at least 12 weeks before planning to get pregnant can help protect a baby against spina bifida by helping to make sure that the baby’s spine develops properly. Folic acid is naturally present in food such as cooked chick peas, broccoli, parsnips, cooked soya and kidney beans and granary bread, but to protect an unborn baby against neural tube defects like spina bifida a woman needs about three times as much folic acid than she can normally get from a regular daily diet.

The Department of Health recommends that any woman planning to become pregnant takes a daily 400 microgram folic acid supplement until the end of the twelfth week of pregnancy. (This may be written as 400mcg, 400 µg or 0.4mg.)

More information

Go to the Midland Fertility Patient Treatment Information page and download:

  • BMI, Weight and Fertility infosheet
  • Diet Plan for PCOS infosheet

LU: 27/5/14 LJB