Does Morning Sickness Mean a Girl? What the Research Really Shows

No. Morning sickness cannot tell you whether you are carrying a girl. The one large study that looked properly found that women carrying girls rated their first-trimester nausea 6.35 on a 9-point scale, versus 6.04 for boys. A real difference, statistically. Also a difference of a third of a point on a scale most people would answer differently on a Tuesday than on a Friday. It predicts nothing about your pregnancy.

Where the idea comes from

It is not pure folklore. Older work had linked the most severe form of pregnancy sickness, the kind needing hospital admission, with female fetuses. So in 2021 Young, La Rosa, Mehr and Krasnow asked whether ordinary nausea showed the same pattern. Their study in Archives of Gynecology and Obstetrics collected retrospective reports from 2,543 mothers about 4,320 pregnancies through an online survey.

Result: girls 6.35, boys 6.04, p = 0.007. The effect survived adjustment for the mother's age, how many children she had already, her general proneness to nausea and, interestingly, whether she already believed in the girl-nausea link. The authors called for more research into why. They did not call it a sex test, and neither should anyone else.

Two things the study cannot do:

• Tell two groups apart when they overlap almost completely. Plenty of women carrying boys reported an 8 or a 9; plenty carrying girls reported a 3.
• Rule out memory bias. Mothers were recalling symptoms after the birth, already knowing the baby's sex.

Here is the claim-by-claim version. The evidence column draws on the Young study and the NICHD's description of early pregnancy signs.

What actually drives how sick you feel

The best current explanation has nothing to do with sex. A 2023 study led by Marlena Fejzo and Stephen O'Rahilly examined a hormone called GDF15, which acts on the brainstem to trigger vomiting. They found that the great majority of GDF15 in a pregnant woman's blood comes from the fetus and placenta, that higher levels go with more vomiting, and that women who had lower GDF15 before pregnancy were more prone to the severe form (hyperemesis gravidarum) because they were less used to it. Women with beta thalassemia, whose GDF15 is chronically high, reported strikingly little pregnancy nausea. In short: how much the fetus makes, and how sensitized you were beforehand.

MedlinePlus adds the everyday amplifiers: the exact cause is unknown, hormone changes or low blood sugar early in pregnancy may play a part, and stress, tiredness, travel and certain foods can make it worse. Nausea is also more common and more severe when you are carrying more than one baby. The Young study found the mother's general tendency to nausea, her age and the number of previous children all mattered independently.

When it starts, when it stops

The NICHD says nausea can begin anywhere from 2 to 8 weeks after conception and, despite the name, can strike at any time of day. MedlinePlus puts the typical course as starting in the first month and continuing through the 14th to 16th week; the Office on Women's Health says it usually tapers off by the second trimester. Some women have it the whole way through. The NICHD notes that among those with the severe form, some feel better after the 20th week and others do not.

One reassuring number, since people ask: in an NIH study of 797 women with positive pregnancy tests, 57.3 percent had nausea by week 8, and those with nausea were 50 to 75 percent less likely to lose the pregnancy. The researchers were careful to say the reverse does not follow. No nausea is not a warning sign.

Practical relief and the full timeline are in When Does Morning Sickness Start and End?

When nausea stops being "normal"

MedlinePlus says to contact your provider if you vomit more than 3 times a day or cannot keep food or liquid down, if your urine is dark and concentrated or you are passing very little, if you vomit blood or material that looks like coffee grounds, if you are losing a lot of weight, or if symptoms are still going strong past the fourth month. The Office on Women's Health describes hyperemesis gravidarum as nausea that does not go away, vomiting several times every day, weight loss, reduced appetite, dehydration and feeling faint; first-line treatment is dry, bland food with fluids, then prescribed anti-nausea medicine, and many women with it need hospital fluids and nutrition through a vein.

If you want to know the sex

Ask your clinician about the ultrasound and blood-screening options where you live and when each is reliable. That conversation takes two minutes and gives a real answer. Counting how often you throw up gives you a number about your stomach, not your baby.

Frequently asked questions

The bottom line

Nausea is about GDF15, your own sensitivity and a handful of everyday triggers, not about whether the baby is a girl. Treat it as a symptom to manage, watch for the warning signs above, and get the sex from a scan. For what actually changes each week, see the pregnancy week-by-week guide.

Official sources

• Young NR et al., Arch Gynecol Obstet 2021 (PubMed): Does greater morning sickness predict carrying a girl? — accessed September 8, 2026.
• Fejzo M et al., 2023 (PubMed): Fetally-encoded GDF15 and maternal GDF15 sensitivity in nausea and vomiting of pregnancy — accessed September 8, 2026.
• NICHD: What are some common signs of pregnancy? — accessed September 8, 2026.
• NICHD: What are some common complications of pregnancy? (hyperemesis gravidarum) — accessed September 8, 2026.
• NICHD news release: NIH study links morning sickness to lower risk of pregnancy loss — accessed September 8, 2026.
• MedlinePlus: Morning sickness — accessed September 8, 2026.
• Office on Women's Health: Pregnancy complications (hyperemesis gravidarum) — accessed September 8, 2026.
• Office on Women's Health: Body changes and discomforts — accessed September 8, 2026.