Just to add: it's not only nowadays that the sex of human fetuses can be identified before birth. The medical technology that makes this possible has been around for a very long time.

Amniocentesis, invented in the 1930s, was first used to determine the sex chromosomes of fetuses in 1960. From 1972, when amnio became much safer because someone came up with the idea of using ultrasound to guide the needle, amnio became commonplace and even standard for women who had medically managed pregnancies if they were over 35 or had a history of certain congenital conditions in their families.

CVS, chromosome and genetic testing on a tiny bit of tissue taken from the placenta that can be done as early as 8-9 weeks, was invented in 1983; I had CVS when pregnant more than 30 years ago.

Fetal scanning by ultrasounds have been in use since the 1960s. They began to become common in medically-managed pregnancies in the 1970s. Due to a constellation of developments that made ultrasound machines much cheaper, more accurate, and portable - and advances in knowledge that allowed physicians and scan technicians to use scans to identify fetal sex with certainty - scans of pregnant women's bellies which reveal the sex of their fetuses in the second trimester have been widely available and used routinely in medically-managed/monitored pregnancies around the world for decades now. In places where sex-selective abortion is practiced, scans have been widely used since at least the 1980s to identify fetal sex even amongst the poor in pregnancies that are not otherwise medically managed.

Now there's the NIPT, a form of genetic testing that allows the sex of fetuses to be ascertained at 8-9 weeks using blood taken from pregnant women's arms in standard blood draws.

So the reality is, medical technology has made it possible to identify the sex of fetuses months before birth for more than 60 years. Over the past 40 years, use of various kinds of medical tech to identify the sex of fetuses in utero has become routine in medically managed pregnancies around the world, as well as in pregnancies of women not getting prenatal medical care. If you're under 40, you come from a "developed" country where your mother had prenatal care when she was pregnant with you, or your mother was pregnant in India or China, then it's very likely that a scan was taken of you showing your sex many months before you were born. Prior to the present century, parents commonly asked scan techs and physicians not to tell them the sex of their fetuses coz they wanted to wait to find out at birth. But the scans showing the fetuses' sex were still routinely done during pregnancy - and the sex was recorded in the medical records months before babies were born.