Pregnancy Week by Week

From the first day of the mother's last period, pregnancy is counted as 40 weeks. Your projected date of birth is intended for reference only. Babies will arrive when they're ready, so be patient.

The sex and hereditary characteristics of the baby are determined at the time of conception.

Although the unborn child spends about 38 weeks in the womb, the usual pregnancy (gestation) lasts 40 weeks. This is because pregnancy is measured from the first day of the woman's last period, and not from the date of conception, which is usually two weeks later.

The three trimesters of pregnancy are as follows:

• Conception to 12 weeks - First trimester
• 12 to 24 weeks - Second trimester 
• 24 to 40 weeks - Third trimester

Conception

The ovum (egg) of the woman is fertilised by the sperm of the man at the time of conception. At that moment, the gender and hereditary characteristics are decided.

• Week 1: This is your menstrual period in the first week. Even if your baby hasn't been conceived yet, this week counts as part of your 40-week pregnancy because your estimated birth date (EDD or EDB) is determined from the first day of your last period.
• Week 2: Fertilization of your egg by sperm will occur by the end of this week.
• Week 3: The cell divides into two thirty hours after fertilisation. The cell (zygote) has divided into 16 cells after three days. The zygote has moved from the fallopian tube to the uterus after two more days (womb). The zygote burrows into the fat uterine lining seven days after fertilisation (endometrium). A blastocyst is a new name for the zygote.
• Week 4: The baby is the size of a grain of rice as it develops. The numerous body systems, including the digestive system, are being formed by rapidly proliferating cells.
• Week 5: As the neural tube develops, it will eventually become the central nervous system (brain and spinal cord).
• Week 6: The infant has been dubbed an embryo. It measures about 3 mm in length. It is secreting hormones that prevent the mother from having a menstrual period at this point.
• Week 7: The heart continues to beat. The placenta and amniotic sac of the embryo have matured. The placenta burrows into the uterine wall to gain access to the mother's bloodstream for oxygen and nourishment.
• Week 8: The embryo is about 1.3 cm long currently. The fast-growing spinal cord resembles a tail. The size of the head is out of proportion.
• Week 9: The eyes, mouth, and tongue begin to develop. The embryo can move around because of the tiny muscles. The liver of the embryo produces blood cells.
• Week 10: The embryo is now referred to as a foetus and is approximately 2.5 cm in length. The organs of the body are all formed. Hands and feet that once resembled nubs or paddles are now developing fingers and toes. Brain waves indicate that the brain is active.
• Week 11: Inside the gums, teeth are sprouting. The small heart continues to grow.
• Week 12: The fingers and toes are distinguishable, but they are still connected by webs of skin. Around this time, a first trimester combined screening test (maternal blood test + baby ultrasound) can be performed. This test looks for trisomy 18 (Edward syndrome) and trisomy 21 (Trisomy 21 syndrome) (Down syndrome).
• Week 13: The foetus can swim fairly well. It has grown to a length of more than 7 cm.
• Week 14: The fully grown eyes have their eyelids fused over them. Because it possesses vocal cords, the newborn can now cry silently. It may start sucking its thumb. Nails are forming on the fingers and toes.
• Week 16: The foetus is around 14 cm long. Tastebuds have appeared on the tongue, as well as eyelashes and brows. If the first-trimester test was not done, the second-trimester maternal serum screening will be offered at this time (see week 12).
• Weeks 18 to 20: An ultrasound will be made available. The purpose of this foetal morphology scan is to look for structural abnormalities, placental position, and multiple pregnancies. Intriguingly, hiccoughs in the foetus are quite common.
• Week 20: The foetus is around 21 cm long. The ears are functional, and they can pick up muted sounds from outside. There are prints on the fingertips. An ultrasound scan can now differentiate the genitals.
• Week 24: The foetus is around 33 centimetres long. The newborn can now open and close his or her eyes because the fused eyelids have separated into upper and lower lids. A layer of waxy secretion protects the skin, which is covered with fine hair (lanugo) (vernix). With its lungs, the infant makes breathing movements.
• Week 28: Your kid is now about 1 kg (1,000 g) or 2 lb 2oz (two pounds, two ounces) in weight and 25 cm (10 inches) in length from crown to rump. The length from crown to toe is approximately 37 cm. The baby's expanding body has caught up with his or her enormous head, and he or she now appears to be more proportionate.
• Week 32: The majority of the time, the baby is sleeping. It has powerful and well-coordinated motions. In preparation for birth, it has most likely assumed the ‘head down' position.
• Week 36: The baby is around 46 cm long. Its head has most likely settled into its mother's pelvis, preparing for birth. If it is born now, it has a good chance of surviving. Over the next three weeks, the lungs develop quickly.
• Week 40: The baby is around 51 cm long and is ready to be born. The actual aetiology of the commencement of labour is unknown. Between the mother and the infant, it's most likely a combination of physical, hormonal, and emotional variables.

Where to get help

• Your doctor
• Obstetrician
• Midwife

Things to remember

Starting on the first day of the mother's last period, pregnancy is counted as 40 weeks. Your projected date of birth is intended for reference only. Babies will arrive when they're ready, so be patient.

The sex and hereditary characteristics of the baby are determined at the time of conception.