How your blood group affects your chances of a baby

More women than ever are now undergoing IVF treatment — the number has risen more than ­tenfold since the early Nineties.

It’s a statistic which is often blamed on the growing trend for postponing ­motherhood until later in life.

But now it seems a woman’s chances of conceiving in her 30s or 40s may not be decided by age alone — her blood type could also affect her fertility, a­ccording to research published

In particular, women with blood type O — the most common type — had a lower egg count and poorer egg quality in their 30s than those with blood type A, say researchers at the Albert Einstein ­College of Medicine in New York.

But how significant are the findings and what are the implications for women planning to start a family in their 30s or later?

Why do we have different blood types?

There are four main blood groups — A, B, O, AB — and several subgroups for each (O, for instance, can be RhD ­positive or negative) and the one you have depends on your genetic make-up.

If both your parents were type O, then you will be O; however, after that there are no hard and fast rules. For example, both your parents could be type A, but you could still end up with type O.

Around 44 per cent of people in Britain have blood group O. Type A accounts for 42 per cent and the balance is made up of less common blood types, including type B and type AB.

The ­difference between the blood types is determined by the kind of ­proteins found on the surface of red blood cells — if you have A type ­proteins, you are classed as group A.

How is fertility linked to blood?

A woman’s blood group appears to influence the amount of a ­hormone called follicle-stimulating hormone (FSH) that she produces. A follicle is a small round cavity — the egg grows in the middle of this.

During ovulation, follicles ­containing maturing eggs push towards the surface of the ovary. There, the ­follicle opens up to allow the egg to drift out. This hormone is released by the pituitary gland, a pea-sized gland in the brain.

Although it plays a vital role in pregnancy — stimulating the ­follicles so they release the eggs — studies show very high levels are a sign of infertility. In particular, they are the sign of something called a low ovarian reserve.

The ovarian reserve is a measure of how many eggs a woman is thought to have left at any one time. It can vary from one woman to another and can be depleted by smoking, ovarian cysts and ­endometriosis, a painful ­condition affecting around two million women in Britain where the cells in the­ ­lining of the womb break down.