Things happen at a steady and fast pace and, by the end of the fourth week, the tiny fetus has its own circulation. Make no mistake, this fetus is still very small: it cannot be seen on the scan. In fact, strictly speaking, this is still an embryo and will remain as such for another four weeks or so before it is appropriately termed a fetus.
The fetus's neural tube will close by the end of six weeks. This is significant where there is a worry about spins bifida. The advice to take folic acid, to reduce the probability of spina bifida, is quite a valid one. However, timing is crucial. If the folic acid is taken starting a week or two after missing a period (or later) it is really useless for this particular purpose. This is why, for those at risk (such as mothers who have previously had a spina bifida baby or pregnancy), the advice is to plan their pregnancy and to start the supplements before conception.
Of course, you cannot guarantee when conception will take place, which may mean taking folic acid for several months. However, this should not be regarded as some kind of burden. Folic acid has so many other benefits.
Gender of the baby
The sex of the baby is determined at conception.
It all depends on the chromosomal make up of the male gamete (sperm) fertilizing the egg.
A woman will always contribute an egg with the same chromosomal constituent, which is 23X. The sperm will either be
23X or 23Y. Of the millions of sperms released at ejaculation, the distribution of the two types is roughly fifty-fifty. Of course, of the millions, only a few hundred reach the egg, and only one will get the privilege of fertilizing it. If it is 23X, the baby will be female; if it is 23Y, the baby will be male. It is that simple.
Sometimes, genetic defects occur which lead to sexual ambiguity. These are very complex and quite uncommon. We would not attempt to address these in this text. However, one interesting fact that deserves mention is that the early gonadal (sex organs) development for both male and female fetuses is indistinguishable. Before the eighth week, the gonads cannot be recognized as male or female.
Can a pregnancy test identify whether the fetus is male or female? The answer is no. A pregnancy test detects a hormone which is the same, whatever the sex of the fetus might be.
Can an ultrasound scan tell the sex- of the baby? Yes, but this does not occur until well into the second trimester. If an expectant mother is having a scan in the first trimester, even at 12-13 weeks, she should not expect the baby's sex to be identifiable on the scan. Even when the image is very clear, the external genitalia of the fetus is so ambiguous at this stage, it is impossible to tell. This is a mere glimpse of what we have tackled in greater detail in the book.