A baby's biological sex is decided at fertilisation by which chromosome the father's sperm contributes — never by the mother, and never by fetal heart rate, placenta position, or anything on an ultrasound report. In India, asking about, revealing, or attempting to determine a baby's sex during pregnancy is also illegal under the PCPNDT Act, a punishable offence carrying both imprisonment and fines.
What actually determines a baby's sex
Humans have 46 chromosomes, including two sex chromosomes — females carry XX, males carry XY. During fertilisation, the mother's egg always contributes an X chromosome, while the father's sperm contributes either an X or a Y:
- X (from father) + X (from mother) → girl (XX)
- Y (from father) + X (from mother) → boy (XY)
The father's sperm is what decides it — not the mother.
Common myths about predicting gender, busted
Two beliefs come up often, and neither holds up:
- "Fetal heart rate under 140 bpm means a boy, over 140 means a girl." Research shows fetal heart rate cannot predict a baby's sex. A baby's heartbeat naturally changes with gestational age, activity level, and other factors that have nothing to do with sex.
- "A posterior placenta means a boy, an anterior placenta means a girl." There's no scientifically proven connection between placental location and a baby's sex.
An ultrasound report never actually states "boy" or "girl." It contains medical information — fetal growth, heartbeat, placental position, amniotic fluid volume, and the baby's overall wellbeing — because that's what the scan is for.
Why sex determination is illegal in India
Under the PCPNDT Act (the Pre-Conception and Pre-Natal Diagnostic Techniques Act), revealing, asking about, or determining a baby's sex during pregnancy is illegal in India. Disclosing or attempting sex determination is a punishable offence that can result in both imprisonment and fines. The purpose of an ultrasound is not to determine a baby's sex — it's performed to assess growth, heartbeat, placenta, amniotic fluid levels, and overall pregnancy wellbeing.
During pregnancy, the focus stays on a healthy mother and a healthy baby, not on sex.
Can IVF or genetic testing reveal or choose a baby's sex?
Scientifically, IVF combined with genetic testing — such as Preimplantation Genetic Testing (PGT) — can identify an embryo's sex. However, in India, the law strictly prohibits sex selection or disclosure of an embryo's sex, even for medical reasons. The purpose of IVF and genetic testing is to improve pregnancy success rates, screen for serious genetic disorders, and help ensure a healthy embryo transfer — not to select for a preferred sex. For more on what this testing actually screens for, see PGT: what it tests for.
The father's role goes beyond just X or Y
Although the mother carries the pregnancy, the father's sperm quality and genetics also play a real role in the child's health:
- Sperm DNA quality — poor sperm DNA, linked to smoking, alcohol, obesity, age, stress or toxin exposure, can raise the risk of miscarriage, certain birth defects, developmental or genetic disorders, and reduced fertility
- Epigenetic factors — a father's diet, exercise, stress levels and exposure to pollution can cause epigenetic changes in sperm DNA that may influence how certain genes are expressed in the baby
- Inherited genes — conditions such as thalassaemia, haemophilia and some metabolic disorders can be passed through the father's genetic line too, which is also why genetic counselling matters in situations like marrying a cousin or close relative
The father's sperm decides whether a baby is XX or XY — not the mother, and not anything she ate, carried, or did differently this pregnancy. Gender should never be something either parent is praised or blamed for.
Frequently asked
Can an ultrasound tell me my baby's gender in India?
Even if it technically shows signs of it, your doctor cannot legally reveal it to you. Under the PCPNDT Act, asking about, revealing or determining a baby's sex during pregnancy is illegal in India and is a punishable offence. Ultrasounds are performed to check growth, heartbeat, placenta and fluid levels — not sex.
Does fetal heart rate predict whether I'm having a boy or a girl?
No. This is a persistent myth. Research shows fetal heart rate cannot predict a baby's sex — it varies with gestational age, activity level and other factors unrelated to sex.
Can IVF be used to choose whether I have a boy or a girl?
Genetic testing used alongside IVF, such as PGT, can technically identify an embryo's sex, but Indian law prohibits using this information to select or disclose sex, even for medical reasons. This testing exists to screen for genetic disorders and support a healthy pregnancy, not for sex selection.
Is a baby's gender ever determined by the mother's body or diet?
No. The mother's egg always contributes an X chromosome; it's the father's sperm — carrying either an X or a Y — that decides the outcome. No diet, posture, or timing changes this.