1. Conception
About 1 in 7 couples in the UK has problems conceiving. After pregnancy, infertility is said to be the most common reason for a young woman to see her doctor.
2. Embryo Growth
On average, female embryos grow more slowly than male embryos during the first week of life.
3. The Law and Mothers
In UK law, the woman who gives birth to a child is its legal mother, regardless of whether she is its genetic parent. For example, even if she received donor eggs, or if she is a surrogate for another couple carrying an embryo to which she is unrelated, she is still the legal mother.
4. Females Carry Females
Eggs are formed before birth and stored in an immature form. This means that a woman who carries a female fetus will also carry its eggs; eggs that may one day make her grandchild.
5. Declining Eggs
Women have the largest number of eggs before they are born, about half way through pregnancy. The peak of 7 million or so declines to around 2 million at birth, and fewer at puberty. The number continues to fall throughout their reproductive years. The menopause occurs when the supply falls below about 1000. In the woman’s life, only at most 400 eggs will be ovulated (1 per month).
6. Detecting Pregnancy
The hormone detected in the pregnancy test, hCG, is produced from a few cells in the developing embryo, but it is produced in such large amounts that it can be readily detected in the mother’s urine at or before the time of the missed period, two weeks or so after the embryo starts developing.
7. Pregnany and Disorders
As women get older, the chances increase of them having a child with certain chromosome disorders, such as Trisomy 21 Down Syndrome. Older women are screened, but younger women are not always screened, which results in more affected children being born to younger mothers.
8. Fertility and Age
The average age of women at first pregnancy is increasing. In western countries, it is currently around 31 years of age. Fertility starts to decline in all women in their thirties, accelerating as they reach the later thirties, and rapidly falling to very low levels in their early forties. The average age of menopause is 51. The average age of patients requesting fertility treatment is also increasing year on year. The reason for this fall is the lower numbers of eggs in the ovaries. The lack of eggs cannot be treated except by using eggs from a donor. Female age is probably the most common cause of infertility.
9. IVF Numbers Around 1.7% of all newborns in the UK are conceived in vitro by IVF or Intracytoplasmic sperm injection techniques.
10. Why Pregnancy is Miraculous
Normally, the embryo inherits half of its genetic material from its mother, who carries it, and half from its father, who is usually genetically unrelated to its mother. The embryo is therefore 'foreign' in an immunological sense to its mother. It is surprising therefore that pregnancy succeeds at all, since if the embryo were a transplant of 'foreign' cells, it would be rejected by the mother’s immune system. This situation is an example of a very specific form of immune reaction that allows pregnancy to take place. Interestingly, a normal successful pregnancy can also result when the mother is totally unrelated to the embryo that she is carrying, for example when donated embryos are used or when the carrying woman is a surrogate mother.
