Human conception was believed by several scientists to have produced more male embryos than those of females, with male embryos having a low chance of survival.
However, a new study proposes that there is an equal number of males and females conceived and female embryos have a low chance of endurance.
“It looks like more females die during pregnancy than males,” said Steven Orzack, a high-ranking research scientist in the Fresh Pond Research Institute in Cambridge, Mass. “People have long thought the opposite was true. An important fact that people thought was reasonably well-demonstrated is probably incorrect.”
A researcher not involved in the study finds the new hypothesis wrong. But Orzack and his associates believe that they are on strong grounds with statistics, which test the long-held conventions on human growth.
Orzack stated that more males are born than females, but females begin to outgrow the number of males as people grow older because males die earlier. This significant occurrence is observed when a person becomes a senior.
“It’s important to study male-female differences in the womb because they underlie, in part, the profound differences we see between males and females at birth and thereafter,” Orzack said.
The researchers of the new study examined records of more than 30 million embryos, fetuses, and babies, taken from the census records of live births. Meanwhile, they also examined the embryos of fetuses and babies that were a product of fertility remedies, underwent testing during prenatal period, or were aborted.
Researchers said that female embryos have a low chance of survival during the first trimester while males are more likely to die during the third trimester.
The data for the new study goes back as far as the 1930s, so it’s hard to tell if modern obstetrics affect the ratio of boys to girls. Orzack said that some parents knew of their unborn child’s gender and they would prefer to abort if it isn’t a boy. “It’s important to study male-female differences in the womb because they underlie, in part, the profound differences we see between males and females at birth and thereafter,” Orzack said.
William James, a voluntary research fellow at the University College London specialized in the gender ratios in the womb declared the new study invalid because most of the data cited is not from healthy women.
The study writer, Orzack responded that” there is no reason to think” that a woman’s health has anything to do with the ratios of males and females.
This is the best kind of data that we can get,” he said, although “it’s not perfect.”
The study can be found in the March 30 issue of the Proceedings of the National Academy of Sciences.
What’s next? “We’d like to pursue research that would help us understand why it appears that more females are dying than males” earlier in pregnancy but then reverses later, Orzack said.