13 December 2021

When can you find out the sex of the baby?

when can you find out the sex of the baby
By the Editorial Comitee IVI Blog

When can you find out the sex of the baby? For many prospective parents, this is one of the most thrilling parts of pregnancy. However, others prefer not to know until the day of birth. For a minority, it is not so much a matter of curiosity and anticipation as a medical necessity to know their baby’s sex. It is so in the case of inheritable sex-linked diseases. Whichever category you fall into, it’s always helpful to understand what determined the baby’s sex in the first place and when during the various stages of pregnancy, or even before pregnancy, you can find out.

In this IVI blog article, we focus on the baby’s sex: at which point it is determined, and the crucial question of when can you find out the sex of the baby. We also look at the various medical methods of finding out and the different circumstances in which they may be indicated.


What determines the sex of the baby?

At the moment of conception, when a sperm meets an egg, your baby’s sex is determined. The egg itself always contains one X chromosome, but the sperm may contain either an X or a Y chromosome. Fertilization by a sperm containing the X chromosome results in an embryo with XX chromosomes which will result in a baby girl. If it is fertilized by a sperm containing the Y chromosome, the embryo has XY chromosomes and will develop male sex organs. It is therefore the sperm that determines the sex of the baby.

Even though the outcome is predetermined at conception, there is in fact no anatomical difference between a male and female embryo at this early stage. Up to around the seventh or eighth week of pregnancy, all embryos have what is called a ‘genital ridge’. This identical set of genitalia will eventually develop into either female or male sex organs. It follows that even if you were able to see the early embryo in an ultrasound scan, it would be too soon to find out whether you’re expecting a boy or a girl.


When can you find out the sex of the baby?

Most prospective parents have to contain their curiosity until around the 18th to 22nd week of pregnancy.  That  is the normal time for carrying out a routine ultrasound scan. Finding out the sex of the baby is not the primary purpose of this. It is generally a check that the fetus is developing in line with expectations no problems are apparent. However, an incidental bonus to the procedure is that usually the ultrasound technician will be able to see whether or not there is a penis. This is not a 100% reliable method because sometimes the position of the baby means it is impossible to see the genital area. It may be possible to find out the baby’s sex even earlier, at around 13 weeks if your doctor recommends an ultrasound scan at this stage. Again, this would not be 100% reliable. For a completely reliable prediction, you would need to turn to one of the methods in which the baby’s DNA is analyzed for a definite identification of its sex.


What are the different ways of determining the baby’s sex?

There are a number of ways that doctors can obtain genetic information about your baby. Knowing its sex is part of the information that can be gained but these tests are never recommended purely for this purpose. They are routinely offered to pregnant women who, for whatever reason, have a higher than normal risk of having a baby with genetic abnormalities.



Amniocentesis is a long-established method of obtaining genetic information by retrieving some of the baby’s DNA. It is normally carried out between weeks 15 and 20 of pregnancy. The procedure involves inserting a needle, guided by ultrasound, into the amniotic fluid surrounding the baby. Analysis of the fluid can indicate whether the baby has one of a number of genetic conditions such as Down’s syndrome, Edwards’ syndrome or Patau’s syndrome. Accuracy levels are good. However, the procedure carries a small risk of causing a miscarriage and many parents-to-be prefer to avoid it for this reason.


Non-Invasive Prenatal Testing (NIPT)

NIPT generally identifies a range of abnormalities similar to those detected by amniocentesis. The difference is that the procedure carries no risk to the pregnancy. It is so as it relies on a blood test taken from the pregnant woman. At IVI we use a type of NIPT which is a cell-free fetal DNA blood test. This is the most comprehensive NIPT available. It identifies conditions mentioned but also many other common abnormalities associated with the X and Y sex hormones. These tests work because during pregnancy, small amounts of DNA from the baby circulate through the mother’s bloodstream. We can access the baby’s genetic information from this source.

There are also more advanced analysis techniques to detect other chromosomal abnormalities. Some are related to the risk of early miscarriage. These would be recommended when medically indicated following identification of some abnormalities during an ultrasound scan.


IVI and preimplantation genetic testing

Finally, for those undertaking a course of in vitro fertilisation (IVF) a technique known as preimplantation genetic testing (PGT) makes it possible to carry out testing of embryos before transfer to the uterus. In some cases it is medically necessary. For example there are certain inheritable genetic conditions linked to either the X or Y chromosome. One of the parents can be a carrier of one of these. In that case, it may be a medical requirement to use PGT. It would allow us to select only embryos of a certain sex. This way we could avoid passing on a condition that is otherwise undetectable.


Contacting us at IVI

For most prospective parents, it’s a personal decision whether to find out the sex of their baby. However, if you have concerns relating to the need for genetic testing, or fertility matters in general, do get in touch. It could be the first step to discovering whether you’re having a boy or a girl!

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