Though you cannot always feel a difference in pregnancy stages on a weekly basis, your baby is developing daily. The further along in your pregnancy you are, the more noticeable these milestones may be. Your doctor may begin asking if you notice certain stages, like feeling the baby move, as you progress in the gestation period.
1st Trimester
Most women aren’t actually pregnant the first two weeks of their gestation period, according to the Mayo Clinic. It can be impossible to know the exact date of conception, so doctors use the first day of your last menstrual period to determine your gestation period. The first trimester will include week 1 through week 14 of your pregnancy. Conception typically occurs around the third week, with implantation occurring in the fourth.
In week 5, the cells develop into an embryo. Organs will begin to form. Basic facial features appear in week 6, and your baby will begin pumping his own blood. In week 7, the face develops more detail, including tiny nostrils. Your baby will start moving in week 8, but you most likely won’t feel it. The arms, legs and toes form the following week. In the 10th week, the neck develops. Your baby will start forming genitals in week 11. Now, it reaches the stage of being a fetus. In week 12, she will have a human profile and will grow fingernails. At week 13, your doctor can most likely hear the baby’s heart beat with a Doppler. By week 14, your baby may be sucking her thumb. The thyroid gland will produce hormones, leading to the prostrate gland forming in males and ovaries forming in females.
2nd Trimester
The Pregnancy website reports the second trimester goes from week 15 to week 27. In week 15, you may feel a fluttering as the baby moves around. The baby learns to breathe in week 16. The following week, fingerprints form. In week 18, the lungs develop air sacs. Most babies will begin a sleep cycle similar to a newborn in week 19. At week 20, you are halfway there. Your baby also develops nerve cells for his five senses during the week. White blood cells begin to form in week 21. The baby can hear at week 22, and his brain cell production will balloon. In week 23, the pancreas will begin producing insulin.
Doctors consider your baby viable at week 24, and the fetus will add weight in muscle and bone mass. The lungs continue to develop with the formation of blood vessels in week 25 and the secretion of surfactant, a type of “grease” that prevents the lungs from sticking together, in week 26. At week 27, your baby’s retinas are fully developed, and she can tell the difference between light and dark.
3rd Trimester
The final trimester of your pregnancy will include weeks 28 to 40 of the gestation period. The developmental growth of your baby tends to slow down, focusing more on the final touches for delivery. According to the American Pregnancy Association website, the fetus will reach 15-to-17 inches in length and weigh 4-to-4½ lbs. from week 28 to week 32. During this time, the baby’s body will begin storing minerals like iron and calcium. Between week 33 and week 36, your baby may move into position for delivery. She will point her head down and continue to put on weight. When you reach week 38, you have reached full-term, which means you could deliver any day. All the baby’s organs have developed, and he is ready for birth.
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