Fertilisation, cycle and pregnancy

From puberty, usually one mature egg is released from an ovary each month. This is ovulation. Before it, the lining of the uterus thickens, getting ready for a possible baby.

Fertilisation and pregnancy. If sperm meet the egg in the oviduct, they may fuse to form a zygote. The zygote divides (by mitosis) as it travels to the uterus, then implants (settles) in the thick lining. This is the start of pregnancy.

IVF. In IVF, an egg and sperm are joined in a laboratory dish. Subhash Mukhopadhyay of Kolkata pioneered India's first test-tube baby in 1978.

The menstrual cycle, as one loop. If the egg is not fertilised, it breaks down after about a day. The thick lining is no longer needed, so it is shed with some blood through the vagina: this is menstruation (a period), lasting 3 to 7 days. Then the cycle starts again:

• it repeats every 21 to 35 days (often about 28);
• ovulation happens around day 14;
• it continues from puberty (ages 10 to 14) to menopause (around age 50).

Periods are a normal, healthy part of life. There is nothing to be ashamed of. As the book says: "Period is your pride."

Menstrual hygiene:

• use clean products;
• change pads every 4 to 6 hours;
• wash your hands;
• wrap used pads before throwing them away; never flush them.

Boy or girl? Females have two X chromosomes (XX); males have an X and a Y (XY). The mother always gives an X. The father gives either an X (a girl) or a Y (a boy). So it is the father's sperm that decides the baby's sex, never the mother.

Pregnancy and birth. Pregnancy lasts about nine months, in three trimesters. From about the ninth week, the growing baby is called a foetus. At birth, the uterus contracts and pushes the baby out. Babies need breastfeeding, warmth and vaccinations. Mothers need nutritious food, rest, regular check-ups, and no smoking or alcohol. More than 10 lakh ASHA workers across India help mothers and babies stay healthy.