And yet, we all know families that are all boys or all girls. It is only rarely that parents have one sex more often than another for some underlying biological reason. Carr said that he understands the psychology of expectant parents wanting to see an image of their baby. Pew Research Center does not take policy positions. Police search for suspects after armed robbery. However, "more and more people are telling us they want to wait until the baby arrives to find out the sex," Carr said. Even while some countries seem to have a disproportionate share of boys, others have particularly high shares of baby girls.
This increase in the sex ratio is driven largely by births in China, where sex ratios have declined slightly in recent years but remain the highest in the world.
Am I Having a Boy or Girl? — Ultrasound & Sex Prediction
The scans are typically done twice during pregnancy, but the one done between 18 and 22 weeks is when the sonographer ultrasound technician might identify the gender of the baby, if parents want to know. Buffalo in Africa have mostly sons when it rains and more daughters when the climate is dry. And yet, we all know families that are all boys or all girls. There is no harm to the baby during the procedure, Carr said. Some birds can influence whether they hatch a male or female chick.