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Blood Test Tracker

Fetal Sex (Cell-Free DNA)

A pregnancy blood test result that reports whether DNA from the baby, found in the mother's blood, includes a Y chromosome. That points to the baby's sex, but it is not perfect.

AI-verified against cited sources. Awaiting expert reviewLOINC 75693-2

What it is

During pregnancy, small pieces of the baby's DNA circulate in the mother's blood. A prenatal cell-free DNA test, often called NIPT or NIPS, reads these pieces. If Y chromosome DNA is found, the report usually says male (XY). If it is not found, the report usually says female (XX). Many labs report this only if you choose to receive it. The same blood sample is mainly used to look at the chance of chromosome conditions such as Down syndrome, so the sex result is an extra.

Why it matters

For most families, the baby's sex is a matter of curiosity. It can matter medically when a family has a condition that is passed on through the X chromosome, because the sex can shape what follow-up is offered. This result comes from a screening test, not a diagnostic test. An ultrasound later in pregnancy or a diagnostic test can confirm the baby's sex. The American College of Obstetricians and Gynecologists says every patient should be offered both screening and diagnostic tests, and each person can accept or decline testing after counseling.

What can affect your result

  • How early in pregnancy the blood was drawn: results before 7 weeks are less reliable
  • Twin pregnancies, where the test cannot reliably tell the sex of each baby
  • A vanishing twin, or other causes of a mismatch such as a difference of sex development, a sex chromosome condition in the baby, or male cells in the mother's own blood
  • Too little baby DNA in the sample (low fetal fraction)
  • Whether you chose to receive the sex result at all
  • Testing very early in pregnancy is less reliable. In a pooled analysis, a male baby was picked up in about 75 of 100 male pregnancies before 7 weeks, about 95 of 100 at 7 to 20 weeks, and about 99 of 100 after 20 weeks.
  • Twin pregnancies: one study found the test had limited use for telling the sex of twins.
  • A vanishing twin (a twin that stopped developing early) can leave DNA in the blood and cause a result that does not match the baby.
  • Other causes of a mismatch include a difference of sex development in the baby, a sex chromosome condition in the baby, and male cells in the mother's own blood (maternal chimerism).
  • Too little baby DNA in the sample (a low fetal fraction) can lead to no result or a less certain result.

The result reflects the current pregnancy only.

When to talk to a clinician

If your cell-free DNA result and a later ultrasound (or your baby's birth) do not match on sex, tell your prenatal clinician or your child's clinician. A mismatch has several possible causes, and doctors recommend looking into it.

Questions you could ask

  • How early in pregnancy was my sample taken, and does that change how sure the result is?
  • If my ultrasound later shows something different, what would we do next?
  • Does the baby's sex matter for any condition that runs in our family?

Questions people ask

How accurate is the fetal sex result?

In large reviews that pooled many studies, cell-free DNA found a Y chromosome in about 95 to 97 of every 100 male pregnancies, and correctly reported no Y chromosome in about 99 of every 100 female pregnancies. Those reviews mostly looked at older methods, and a blood draw very early in pregnancy was less reliable. Your lab can tell you how accurate its own test is.

Why does my report say "no result" or "not reported"?

Most labs report fetal sex only if you choose to get it. A report can also show no result if the sample did not have enough baby DNA or if the lab could not read the sex chromosomes clearly. Ask your prenatal clinic which applies and whether a repeat blood draw would help.

What if the result does not match my ultrasound?

Tell your prenatal clinician. A mismatch can have simple causes, such as a vanishing twin or a draw very early in pregnancy, and sometimes it points to something that needs a closer look. Your clinician may suggest repeating the ultrasound or doing further testing.

Show the science and sources

For clinicians and researchers

Cell-free DNA tests report fetal sex by finding Y chromosome sequences in maternal plasma, either with PCR or by counting chromosome-specific DNA fragments (LOINC 75693-2, method "Dosage of chromosome specific cell free (cf) DNA"; its answer list is male fetus, female fetus, no result). In a meta-analysis of 57 studies (3,524 male-bearing and 3,017 female-bearing pregnancies), detection of Y sequences had a sensitivity of 95.4% (95% CI 94.7-96.1%) and a specificity of 98.6% (98.1-99.0%), with a positive predictive value of 98.8% and a negative predictive value of 94.8%. Sensitivity was 74.5% before 7 weeks, 94.8% at 7 to 12 weeks, 95.5% at 13 to 20 weeks and 99.0% after 20 weeks, and tests on urine were unreliable (Devaney 2011). A second meta-analysis of 90 studies and 10,587 results found a mean sensitivity of 96.6% (95% credible interval 95.2-97.7%) and a mean specificity of 98.9% (98.1-99.4%), with little variation by trimester (Wright 2012). Both reviews cover mostly PCR-based assays from before genome-wide sequencing was common, so a lab's own validation figures matter more for a specific report. Reported causes of a mismatch between cfDNA sex and the newborn's sex include vanishing twin, differences of sex development, sex chromosome aneuploidy and maternal chimerism (Byers 2019). In a referral-practice cohort, abnormal sex chromosome cfDNA results were linked to IVF and twin pregnancies, and the authors concluded that cfDNA has limited utility for sex prediction in twins (Scibetta 2017). The American College of Medical Genetics and Genomics strongly recommends cfDNA screening over traditional methods for trisomies 21, 18 and 13 in singleton and twin pregnancies and strongly recommends that it be offered for sex chromosome aneuploidy (Dungan 2023). This marker covers only the reported fetal sex; screening results for sex chromosome conditions are reported separately.

LOINC 75693-2 (primary), 75668-4. Specimen: plasma.

Sources

  1. Noninvasive fetal sex determination using cell-free fetal DNA: a systematic review and meta-analysis, JAMA (2011)
  2. Non-invasive prenatal diagnostic test accuracy for fetal sex using cell-free DNA: a review and meta-analysis, BMC Research Notes (2012)
  3. Discordant sex between fetal screening and postnatal phenotype requires evaluation, Journal of Perinatology (2019)
  4. Clinical accuracy of abnormal cell-free fetal DNA results for the sex chromosomes, Prenatal Diagnosis (2017)
  5. Noninvasive prenatal screening (NIPS) for fetal chromosome abnormalities in a general-risk population: an evidence-based clinical guideline of the American College of Medical Genetics and Genomics (ACMG), Genetics in Medicine (2023)
  6. Screening for Fetal Chromosomal Abnormalities: ACOG Practice Bulletin, Number 226, Obstetrics & Gynecology (2020)
  7. LOINC 75693-2 with answer list (NLM Clinical Tables API), National Library of Medicine / Regenstrief Institute

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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