It is hard to point the exact moment when the sperm meets the egg, what is easier to point though is the first day of the last menstruation, which allows the doctor to calculate the due date, counting 40 weeks.
When first conceived, the baby, being made up of just a few cells, is often referred to as an embryo, until it reaches its eighth week, and is then referred to as a fetus (or baby). Development begins when the fertilised egg attaches itself to the wall of the uterus during implantation.
By the end of the first trimester the fetes normally will be approximately 6-7,5 cm in length, and weight about 30 grams.
During this stage we face development of:
- placenta and umbilical cord which brings nutrients from the mother to the baby (and removes waste products from the baby to the mother’s body)
- amniotic sac, a fluid-filled membrane that cushions the developing fetus
- all major organs including the heart which begins to beat around 25th day after conception
- neural tube (which goes on to form the brain and spinal cord) limb buds (the beginning of arms and legs)
- fingers, toes, ears, ankles, wrists, eyelids
- various systems are being created, but they have quite simple/ primitive forms
As the pregnancy progresses, a baby might begin to seem more real. We might hear the heartbeat at the prenatal appointments, and enlarging abdomen might force women to put away their favorite jeans.
While a Mum-to-be is adjusting to the changes in her body, fetal development takes on new meaning. Two months ago, the baby was simply a cluster of cells. Now he or she has functioning organs, nerves and muscles.
The second trimester is a period where the developing baby becomes active.
During that time a baby begins to move, kick and swallow. Around 14th week the sex is formed and visible. After 15th week the baby grows rapidly. The baby’s skeleton is developing bones, which will become visible on ultrasound images in a (few weeks.
Around fifth month the baby is able to turn from side to side. The moves can be experienced easily. Also in this time the baby begins to sleep at regular intervals. By the end of the second trimester the fetus is around 20 cm long and weights up to half kilogram. The baby can open eyes as a reflex, but cannot see yet. With the help of medical support a baby is able to survive outside of the uterus.
The baby starts being aware of the surroundings. It gains a lot of weight. Twenty-nine weeks into the pregnancy, or 27 weeks after conception, the baby’s bones are fully developed, but they’re still soft and pliable.
Around the 30th week the baby’s eyes are wide open a good part of the time.
It might have a good head of hair by this week. Red blood cells are now forming in the baby’s bone marrow.
By now (s)he might be more than 27 centimeters long from crown to rump and weigh nearly 1,300 grams. It can suck the thumb. It starts seeing light, hearing voice and Mom’s heartbeat. The features of the face have been shaped. The baby’s nervous system is developing really much and also (s)he can breath using his/her, lungs.
At the end of the third trimester the baby moves into the position of birth (head down), lowering down in the mother’s abdomen, nearer to the pelvis.