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  • The 40-week period of pregnancy is taken to be the beginning of the mother’s last period. This is only a guideline. Babies will arrive when they are ready. You need to be patient.
  • At conception, the gender and inherited characteristics are determined.

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Unborn babies spend around 38 weeks in the womb. However, the average length of pregnancy (gestation), is 40 weeks. Because pregnancy is measured from the first day after a woman’s last period and not the date of conception (which is usually two weeks later), this is a common error.

Pregnancy can be divided into 3 trimesters:

  • First Trimester Conception to 12 Weeks
  • Second Trimester 12 to 24 Weeks
  • Third trimester 24 to 40 weeks


Moment of conception occurs when the man’s egg (or ovum) fertilizes the woman’s eggs. In that moment, the gender and inherited characteristics of the baby are determined.

Week 1

Your first week of menstruation is the actual start of your period. Your expected birth date (EDD, or EDB), is calculated starting on the first day of each month. This week counts as part your 40-week-long pregnancy, even if your baby hasn’t been conceived yet.

Week 2

The fertilization of your egg with sperm will occur at the end of the week.

Week 3

The cell splits in two thirty hours after conception. Three days later, 16 cells have formed from the cell (zygote). Two more days later, the zygote had migrated from its fallopian tube into the uterus (womb). Seven days after conception, a zygote burrows into the plump uterine tissue (endometrium) seven days later. The blastocyst is the name given to the zygote.

Week 4

A baby’s development is much smaller than a grain rice. These cells are rapidly growing and forming various body systems including the digestive system.

Week 5

The developing neural tube will eventually turn into the central nervous system (brain, spinal cord).

Week 6

The embryo is the name given to a baby. It measures approximately 3 mm in height. It is around 3 mm in length.

Week 7

The heart beats. The embryo has created its amniotic sac and placenta. To access nutrients and oxygen from the mother’s bloodstream, the placenta burrows into the uterine wall.

Week 8

The embryo measures approximately 1.3 cm long. The spinal cord is rapidly growing and looks almost like a tail. The head is large.

Week 9

The embryo is forming its eyes, mouth, and tongue. The embryo can move around with the tiny muscles. The embryo’s liver is responsible for making blood cells.

Week 10

The embryo, also known as a Fetus, is approximately 2.5 cm long. The body is fully formed. The hands and feet were once shaped like paddles or nubs. Now they are evolving into fingers and toes. Brain waves are active, and the brain is active.

Week 11

The gums are bursting with teeth. The tiny heart continues to develop.

Week 12

Although fingers and toes can be identified, they are still connected by webs of skin. This is the time to perform a combined screening test for the first trimester (maternal blood tests + ultrasound of baby). This test can be used to check for trisomy 18 or 21 (Edward Syndrome span>).

Week 13

The fetus is able to swim quite vigorously. It now measures more than 7cm in length.

Week 14

The fully developed eyes have their eyelids fused. Because it has vocal chords, the baby can now muffle its own voice. The baby may even begin sucking its thumb. It is growing nails in its fingers and toes.

Week 16

The average length of a fetus measures around 14 cm. The fetus has eyelashes and eyebrows, and the tongue now has tastebuds. If the first trimester screening was not completed, the second trimester maternal serum screening is offered. (see week 12 span>

Week 18-20

An ultrasound will also be provided. This scan will check for structural abnormalities and position of the placenta. It is common to observe hiccups in the fetus.

Week 20

The average length of a fetus measures around 21 cm. The ears can hear muffled sounds outside and are fully functional. The fingertips are covered in prints. An ultrasound scan can be used to distinguish the genitals.

Week 24

The average length of a fetus measures around 33 cm. The baby can now open and close its eyes by separating the fused eyelids into lower and upper lids. The skin is covered with fine hair (lanugo), and protected by waxy secretion layer (vernix). The baby breathes with its lungs.

Week 28

Your baby is now approximately 1 kg (1, 000 g), or 2 lb 2oz (2 pounds, 2 ounces) in weight and measures 25 cm (10in) from crown to tail. From crown to toe, the length of your baby is approximately 37 cm. The baby’s growing body has caught up to the large head, and now appears more proportionate.

Week 32

Sleeping is the most common activity for a baby. Its movements are coordinated and strong. In preparation for the birth, it has likely assumed the “head down” position.

Week 36

The baby measures approximately 46 cm in height. The baby has likely positioned its head in its mother’s pelvis ready to give birth. Its chances of survival are high if it is born right away. The next few weeks will see rapid development of the lungs.

Week 40

The baby measures approximately 51 cm in height and is ready to be born. The exact cause of labor is not known. Most likely, it is a combination physical, hormonal, and emotional factors between the baby and mother.

Where can I get help

  • Your doctor
  • Obstetrician
  • Midwife

Things to Remember

  • The 40-week count for pregnancy starts on the day the mother has her last period. This is just a guideline. Babies will arrive when they are ready so be patient.
  • At conception, the gender and inherited characteristics are determined.


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