Most Reliable Methods Of Predicting The Fetal Sex, And Why?

The most reliable methods of fetal sex prediction (commonly referred to as gender) are those which examine genetic material from biological tissues of the baby, placenta, or placental precursors. For the majority of expecting parents who want to know their baby’s sex, that method will take the form of prenatal cell-free DNA (cfDNA) screening for sex chromosome information.

While different cfDNA products exist for various purposes, such as non-invasive prenatal screening (NIPS) for chromosomal variations like trisomy 21 (Down syndrome), cfDNA screening for fetal sex is technically possible as early as 6 or 7 weeks gestation. By checking the pregnant person’s blood sample for the presence or absence of Y chromosome material, cfDNA screening laboratories can offer curious parents-to-be an early glimpse at whether the baby’s chromosomal sex is male (Y chromosome detected) or female (no Y chromosome detected).  

These methods are safe, well-studied, and very reliable – for example, with the Juno Birch™ test and its protocol for at-home sample collection with just a few drops of blood from a finger-prick, patients can expect >99% accuracy.

Diagnostic testing during pregnancy

Parents seeking diagnostic-level information about their baby’s chromosomes might choose to schedule a chorionic villus sampling (CVS) or amniocentesis procedure with a specially-trained obstetrician called a Maternal Fetal Medicine (MFM) specialist. With both CVS and amniocentesis, performed in the first and second trimester, respectively, samples from the procedures are sent to a cytogenetics laboratory for diagnostic testing such as a karyotype analysis or chromosomal microarray analysis (CMA). 

These tests examine whole, intact chromosomes from multiple cells of the pregnancy, and can confirm whether the pregnancy has the expected amount of genetic material. Since both CVS and amniocentesis are invasive medical procedures, carrying a small (but not insignificant) chance for pregnancy loss following the procedures, it’s pretty uncommon for a pregnant person to have a CVS or amniocentesis solely to learn fetal sex information. 

Fetal sex and in vitro fertilization

Some parents having fertility treatment through in vitro fertilization (IVF) may choose to screen their embryos for chromosome variations using a technology called pre-implantation genetic testing for aneuploidy (PGT-A). This practice requires a biopsy of very early embryos (usually day 5 or day 6) so the biopsied tissue can be sent to a special laboratory for screening; meanwhile, the biopsied embryos will be frozen as the parents and their fertility doctor await the results. PGT-A isn’t possible for all IVF patients, since results are not available quickly enough for a fresh embryo transfer.

While PGT-A can often be helpful in choosing which embryos are most likely to result in a successful transfer and, ultimately, a successful pregnancy, it’s costly and not guaranteed to be 100% accurate. Since the part of the blastocyst that’s biopsied in PGT-A would otherwise go on to become the baby’s placenta and not the baby itself, occasionally the chromosomal makeup in these tissues won’t be identical to that of the baby.

Statistically, it’s much more likely to see these types of chromosomal discrepancies involving chromosomes other than the sex chromosomes (X and Y) – so usually, PGT-A will be very accurate in predicting fetal sex. However, many fertility doctors and ethics experts consider PGT-A for sex selection (that is, choosing which embryo to transfer based on sex alone) to be somewhat controversial, and this practice may not even be allowed in certain countries.

Since chromosomal sex, anatomic sex, hormonal sex, and gender identity are each complex, there are limitations to every method of fetal sex prediction. Even prenatal ultrasound isn’t perfect, despite being the most common method for fetal sex prediction in the past two decades. It’s important to consider what’s most important to you when making a decision about learning the sex of your baby.

How, when, and where you learn may all make a lasting impact on your memory of this special early bonding experience, should you choose to learn before birth.

Still, waiting to learn the sex of your baby? You may be able to find out sooner than you think! Click here to read more about our Juno Birch™ Fetal Gender Test.

- Authored by Katie Sagaser, MS, LCGC

JunoDx.com and the materials and information it contains are not intended to be and do not constitute medical advice, other health advice, or diagnosis.  Do not use JunoDx.com or the materials and information published at JunoDx.com as a substitute for medical care and treatment. You should always consult with a qualified physician or healthcare provider about your specific circumstances.