Boy or Girl? How a Baby's Sex Is Determined
A baby's sex is set at fertilisation by whether the sperm carries an X or a Y chromosome. It is natural chance, not the fault or choice of either parent.
In this article 4 sections
Whether a baby will be a boy or a girl is decided at the moment of fertilisation, by whether the sperm that joins the egg carries an X or a Y chromosome. This is entirely a matter of natural chance; neither the mother nor the father can choose it, so there is no reason to blame anyone. In the video, Dr Sharmin Afroz explains this topic briefly. There are many misconceptions about this in our society, so it is important to understand the simple science.
01What chromosomes are and how sex is decided
Every cell in the human body holds genetic information in tiny structures called chromosomes. One pair of these determines the baby’s sex: the X and Y chromosomes.
- Women have two X chromosomes (XX), so every egg from the mother always carries an X.
- Men have one X and one Y (XY), so some of the father’s sperm carry an X and some carry a Y.
- If a sperm carrying X joins the egg, the baby is XX, a girl.
- If a sperm carrying Y joins the egg, the baby is XY, a boy.
02So is the father responsible?
Scientifically, it is true that the X or Y chromosome comes from the father’s sperm. But that does not mean the father is ‘responsible’ or decides anything. Millions of sperm are released at once, and no one can control which one reaches the egg. In each pregnancy, the chance of a boy or a girl is roughly equal, and having had a boy or a girl before does not change the chance next time.
Sadly, in many families the mother is blamed when a daughter is born. This is scientifically wrong and causes the mother deep emotional distress. Blaming the father is equally unfair. Boy or girl, every child is equally precious.
It is important for the whole family to understand this simple science. Worry and stress during pregnancy are not good for the mother or the unborn baby. So the husband and other family members should support and reassure the mother, so that she can have a calm, healthy pregnancy. A healthy child should be the greatest wish.
03Common myths
- Eating certain foods, fruits or drinks leads to a boy or a girl: there is no evidence for this.
- Having sex on particular days of the cycle guarantees a boy or a girl: this is not reliable either.
- The shape of the bump, the mother’s looks or food cravings reveal the sex: these are only folk beliefs.
- Traditional or home remedies cannot change the sex; untested products may even harm mother and baby.
Note that sex determination or abortion purely to choose a boy or a girl goes against medical ethics and is illegal in many countries.
When to see a doctor
What matters most in pregnancy is the health of mother and baby, so attend regular antenatal check-ups. Also talk to a doctor in the following situations:
- If there is a family history of an inherited condition linked to the baby’s sex, for genetic counselling
- If family pressure about the baby’s sex leaves you anxious, low, sleepless or depressed
- If you have bleeding, severe abdominal pain, fever or reduced baby movements in pregnancy, go to hospital without delay
Q & A
Frequently asked questions
Not at all. The mother's egg always carries an X; the baby's sex depends on which sperm joins it, which no one can control.
No. There is no evidence that any food, medicine or home remedy can determine a baby's sex.
Each pregnancy is separate; the sex of earlier children does not change the chance next time.
At the moment of fertilisation, when the sperm and egg join, the baby's sex is already set.
Article & video by
Dr. Sharmin Afroz
Obstetrics, Gynaecology & Infertility Specialist and Laparoscopic Surgeon
Assistant Professor, Department of Obstetrics & Gynaecology, Anwer Khan Modern Medical College & Hospital.
