1. Why are fertility rates different among different races?
Geographic and cultural differences are far more important than racial ones. Just think about what has happened to fertility in Quebec over the last 50 years, with the reduced influence of the Catholic church and the advent of contraception. Similar trends have been seen in Italy, Spain, and even Latin America. China's fertility rate is very low because of its one-child policy. Although fertility remains relatively high in sub-Saharan Africa, that is almost entirely due to poverty, high infant and child mortality, and low access to contraception, rather than race.
2. How do you determine gestational age? How accurate is it?
The two major ways are (1) based on the first day of the last menstrual period (which is not bad if asked soon after the woman is known to be pregnant and she has monthly periods with a highly consistent menstrual cycle length); and (2) ultrasound measures of the length or head size (biparietal diameter) in the first half of pregnancy. Of the two, the ultrasound estimate is usually more accurate.
