Probabilities and Counselling

The chance of a chromosomal problem increases with age (all kinds, not just Down's syndrome).   Originally, amnios were done blindly, and needle sizes were relatively large, a situation in fraught with hazard. The notion that amnios are offered to women age 35 and above at delivery comes from a calculation in the pre-ultrasound era - the age at which the risk of finding a chromosome problem becomes higher than the risk of injury from an amnio. The same calculations done now bring the maternal 'safe' age down to 18!   There is no genetic switch that turns on at age 35. That birthday is an arbitrary way station along a progressive incline of genetic risk. Most instances of chromosome problems occur in younger women, because that is when pregnancies tend to happen.

Studies on the ethics of prenatal diagnosis have concluded that amniocentesis should be offered to all pregnant women. Risk calculations include a hidden assumption that "odds" have a meaning for individual patients. Statistics applies to populations. The bigger the population, the more exact the numerical description. That is helpful for a health care organization and for research, but it is not especially meaningful for an individual. Does a risk of 1:100 mean that someone is ten times calmer than when the risk is 1:10? Of course not. Once any risk of a terrible problem is raised, anxiety becomes worse and worse (especially when a woman's hormone levels are sky high!). Peace of mind comes from knowling exactly what is going on, normal or otherwise.

The "balloon" just above and behind the head is the (secondary) yolk sac, which makes blood and immune competent cells and functions as an outboard energy source for an embryo. The yolk sac is the first structure to be seen, appearing just two weeks after conception. A yolk sac that is flat or distorted, too big, too small, or absent are all clues to serious problems in the first few weeks.. We do a lot better six weeks after conception and subsequently, as organ systems are forming, and their features become visible by high resolution ultrasound imaging. Nuchal translucency (NT) has received a lot of attention as an ultrasound screening method, late in the first trimester, eventhough many other features can be evaluated by that time. Only an amnio provides 100% reliable information about the presence or absence of a chromosomal disorder.

Early Pregnancy Loss