Mother and baby

Female fertility depends upon several factors. Some factors can be altered by lifestyle choice, some can be adjusted by treatment and some are not adjustable but are important as they affect the chance of conception and may therefore alter your choice of treatment.

Lifestyle choice


There is plenty of evidence to show that fertility is affected and altered by body mass. This is best determined by your body mass index (a calculation based on height and weight –you can calculate this on the NHS website by clicking here).

If your body mass index is 20-25 this is normal. If it is 25-30 you are overweight and if it is 30-35 you are obese. Over 35 is considered significantly obese.

If your body mass index is over 28 it will start to affect your fertility. If it is over 30 it will have a significant effect and also an adverse effect on any treatment. You will need a higher dose of medication. If your body mass index is over 32 then not only will it further affect your chance of pregnancy but also it will increase your risk of miscarriage by up to 30%.

Even if your cycle is normal excess weight affects the time it takes for women to conceive. If you are overweight or obese it takes significantly more menstrual cycles on average to conceive than if your BMI is normal. The Higher the BMI the longer it takes. For example it takes 9 months for 75% of a group of women with normal BMI and regular cycles to conceive. For overweight women it is 12 months and for obese women it is 18 months to achieve the same result. This is reversible.

Excessive weight can have a direct effect on ovulation and may suppress it. You make oestrogen in your peripheral fat so if you have more of it you will have more oestrogen produced which may interfere with ovulation, It may either suppress your periods, make them irregular and/or make them heavier. Because your height is by now fixed the only thing you can do to reduce your body mass is to lose weight.

If you are overweight you should give serious thought to losing weight before trying for pregnancy and certainly before embarking upon any treatment. Speak to your GP, as there are now many programmes to assist you.

Low body mass can also be a problem but is much more unusual in fertility clinics. Usually this affects ovulation.

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Smoking has a toxic effect upon the embryo. This is also seen in pregnancy where it can also lead to restrictions in your baby's growth and development.

There is ample evidence to show that smokers take longer to conceive than non-smokers. If you smoke it takes you on average twice as long to conceive than if you do not. If you want to improve your chance of getting pregnant there is only one piece of advice. You must stop smoking.

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If you or your partners work/social arrangements etc mean that you are apart for periods of time or parts of the week you need to look at these arrangements. If you are not having sex around the time of ovulation you are much less likely to conceive. Look at your timetable and make sure that this is not affecting your chance of pregnancy. If you have to choose between income and pregnancy be sure to discuss this and do not let too much time pass without at least confronting the issue.

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Treatments are available for ovulation disorders, tubal disorders, endometriosis and unexplained infertility. These are detailed in the appropriate section. All treatments need to be balanced against your natural chance over the same period of time. For example if you ovulate naturally then ovulation treatment will probably not help you and might even reduce your chance of pregnancy. Treatments such as IVF might give a better pregnancy rate than your natural chance (i.e. 3+ years trying ) or a worse chance than your natural chance (i.e. 1 year trying) dependant on results of investigation and previous treatments.

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Factors outside your control

Female age is the single most important predictor for fertility. You cannot control your age and fitness only moderates age changes slightly. Fertility declines slightly after 35. This is more pronounced after 38 and the reduction is rapid after 40. There are no reports of IVF livebirths in the UK after the age of 46. Ones you might hear about are all using donated eggs from another woman. The only thing you can do is to make decisions about whether you wish to try to conceive and how far you would be prepared to go. Decide which treatments are acceptable and which are not. Whilst you should not be forced into making a premature decision make sure that age is a consideration that you consider when making your choice.

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Investigations offered

Investigations are aimed at identifying factors that might reduce female fertility. Tests for ovulation, polycystic ovarian syndrome, endometriosis and tubal disease are described in the relevant sections.

Tests for future fertility are not covered here as it is assumed that people are already trying to conceive now.

Ovarian reserve

Recently it has been possible to accurately measure ovarian reserve. This tells you if you have a large, small or minimal number of eggs left. The relevance of this is

  1. It may help you decide whether a treatment is worthwhile
  2. Is your reserve appropriate for your age?
  3. What the chance of achieving sufficient stimulation to complete an IVF/ICSI cycle is?
  4. If you have an excessive reserve- what the risk of OHSS is
  5. Optimising drug regimens for individuals undergoing IVF/ICSI

The main test of ovarian reserve is Follicle stimulating hormone (FSH). This hormone stimulates the ovary. When the ovary responds the gland (pituitary gland) producing FSH senses this and reduces FSH production so normally there is a balance. If the ovary does not respond to FSH then no response is detected and even more FSH is released. If your FSH level is high then your ovaries are working less well. If however you ovulate either in response to treatment or on your own despite a high FSH level your chance of pregnancy is not reduced. If however you do not ovulate in response to any treatment your chance of conception is low.

An older test is Clomiphene challenge where people are given Clomiphene and their FSH is tested before and afterwards. This is now obsolete.

Currently the two best tests are Antral Follicle Count, which is calculated by Transvaginal Ultrasound, and Anti Mullerian Hormone (AMH) measured in the peripheral blood.. Both tests are more sensitive than FSH.

Antral follicles

Antral follicles measure 2-8mm. The test is usually done soon after menstruation has commenced and measures the number in both ovaries. A count of fewer than 4 indicates poor prognosis. The normal is 15-30.

Anti-mullerian Hormone

AMH determines if the level is in the optimal, low or minimal/undetectable range. The lower the level, the less the reserve. This test is not timed to any particular part of the menstrual cycle.

Very high levels are seen in Polycystic Ovarian syndrome and these also correlate with a higher risk of OHSS with ovarian stimulation.

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