Almost since its beginning in the 1970s, in vitro fertilization (IVF) has been surrounded by controversy. However, many concerns faded away as more children were born healthy with the help of IVF.

ivf controversy

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But a new controversy has arisen since model and television host Chrissy Teigen announced that she and her husband, singer John Legend, used IVF to choose the sex of their child.

“Not only am I having a girl,” Teigen told People, “but I picked the girl from her little embryo. I picked her and was like, ‘Let’s put in the girl.’”

Read More: The Basics of In Vitro Fertilization »

How Sex Selection Works

Selecting the sex of a baby is not as difficult as it might seem, especially with recent advances in IVF.

During IVF, several eggs are removed from a woman’s body. Then, in a laboratory, the eggs are fertilized with sperm to create embryos that can be implanted into a woman’s uterus.

Before the eggs are implanted, a doctor can remove a single cell from the embryo to look at its chromosomes. This is known as preimplantation genetic diagnosis (PGD).

PGD is used to check the embryo for serious or fatal genetic disorders and can also reveal the embryo’s sex.

This makes it possible for potential parents to say “boy” or “girl” before an embryo is implanted.

Read More: More Cycles Equals More Success in IVF »

Selection Still Rarely Used

The United States has no restrictions on IVF for sex selection. However, some countries have banned its use except when there is a risk of a sex-linked genetic disorder.

In spite of its availability, the use of sex selection is limited. This might be due to its high price tag — IVF with PGD costs between $15,000 and $25,000 per cycle.

“The number of patients, and particularly the number of offspring that are born following IVF and PGD for nonmedical sex selection, without any other indication, is very, very low,” Judith Daar, J.D., a professor of law at Whittier Law School, told Healthline.

Exactly how low is not clear. Clinics are not required to report the reasons couples use IVF.

Then a 2008 study from Johns Hopkins University provided a glimpse of how common IVF with PGD is. Forty-two percent of clinics offering these procedures reported providing sex selection for nonmedical reasons.

An earlier survey found that only 8 percent of people who responded said they would use IVF or another technology to choose the sex of the embryo for nonmedical reasons.

IVF sex selection is not free of ethical or moral questions. The American Society for Reproductive Medicine (ASRM) outlined many of these concerns in a 2015 report.

“We thought it was important for clinics to have available the arguments that surround the technology,” said Daar, who is a member of the committee, “but we leave it up to the individual providers to make a decision about their practice.”

Read More: Lower Birth Rate for Frozen Eggs, Study Says »

Medical Concerns Arise

There is nearly 100 percent accuracy of IVF sex selection, yet this procedure still carries the same risks to women and children as IVF used for medical reasons.

When women choose to have IVF for medical reasons — such as infertility — doctors balance the risks with the benefits of the procedure.

If choosing the sex of the child is the only reason for undergoing IVF, women still need to understand the risks.

Some people are also concerned that nonmedical use of IVF for sex selection may tie up medical resources and prevent couples with infertility from getting the help they need.

This may not be an issue in the United States where IVF sex selection is not that common. However, it could cause problems in countries with more limited resources and a high demand for sex selection.

Read More: U.K. Scientists Given OK to Use Gene Editing on Human Embryos »

Social Concerns Arise

Others see nonmedical IVF sex selection as discriminating against one sex or the other.

To avoid discrimination, some clinics limit the use of nonmedical IVF to parents who already have at least one child. In a Johns Hopkins study, 41 percent of clinics took this approach.

Extensive use of IVF sex selection to choose one sex could also throw off the natural balance between males and females in society.

This effect may be unlikely in the United States. A 2004 survey found that most people who responded did not have a strong preference for having a boy or a girl. Fifty percent wanted a family with an equal number of boys and girls while 27 percent had no preference.

A broader concern over IVF sex selection is that it may open the way for parents to select embryos based on other traits — what the ASRM ethics committee called a slippery slope.

Without laws or guidelines governing this technology in the United States, the question of how it is used and how many problems it creates lies in the hands of the clinics.

“Clinics are in a position to make individualized decisions about the provisions of this type of technology,” said Daar.