Fearfully and wonderfully made - there's no question about it - the growth and development of an infant from conception through birth is nothing short of miraculous. Following a pregnancy week by week a person can "see" how quickly the physiologic changes occur, especially during the first trimester. It is now possible to follow the development of a baby through pictures, diagrams and ultrasound scans and with the advent of the 4D ultrasound, it is now possible to see the baby in the womb with perfect animation and depth. It is amazing to see the response to stimulation at a very early stage in gestation, information that nullifies the idea that babies in the early stages of development are basically inert. Technology has delivered some amazing methods in this area.
A pregnancy is usually measured in terms of weeks, with 40 weeks gestation being the end of the pregnancy, the official due date. However, many people refer to pregnancy in months and then break the months into trimesters. There are three main stages of fetal development - conception, embryonic development and the development of the fetus. The first two stages fall under the first trimesters and the rest under the second and third trimesters.
The first trimester begins with conception, which usually occurs in week two of the pregnancy. The two weeks prior to conception are used by the body to prepare the womb for the potential pregnancy by lining it with blood rich tissue. After conception the fertilized egg makes its way to the uterus where it implants and begins to grow.
The next stage is the most crucial stage in fetal development. The embryonic development stage is the time when the systems of the body are in the foundational stages. The embryo begins the intense and profound growth during this period, which lasts until the 11th week of gestation. At four weeks, cellular division continues and those cells that will make up the placenta divide away from those that will make the baby. By the time the embryo is six weeks, the heartbeat has already begun and limbs are developing. By eight weeks, the intestines have started to form, teeth are growing under the gums and by the time the end of this trimester has come around, the baby has developed joints and the irises of the eyes are taking shape. The central nervous system and major organs are being developed during this period.
The term fetal development, while used to describe the fetus' development over the entire pregnancy, really applies to the period of the second and third trimesters - beginning at week 11 and continuing through to childbirth. From the 11th through the 16th week the fetus begins to develop hair, nails, vocal chords, and you can distinguish the genitals. By the 16th week an ultrasound can show whether the mother is having a baby girl or a baby boy. It is also during this time that movement can often be felt. Kidneys begin to process body fluids and the liver begins its function. Bones harden during this period as well. Beginning at the 16th week through the 20th week, the baby goes through a growth spurt. Fat begins to develop under the very thin skin and the heart is pumping about 25 quarts of blood each day. Meconium collects in the bowel and baby is awake and asleep in a behavior pattern that will continue after birth. During this part of the pregnancy an amniocentesis is sometimes done to determine birth defects.
Things slow down during the 21st through 24th weeks and some of the finer details of the baby's body are formed. Eyelids and eyebrows, the testes (if the baby is a boy) will begin to descend, and baby will continue to gain weight. At the end of this trimester, the baby will weigh somewhere in the neighborhood of 1.3 pounds (.6 kg).
Entering into the third and final trimester, baby is busy working on lung development in order to transition to breathing air rather than taking oxygen from blood. Between weeks 25 to 28, most of the energy is spent here. After 28 weeks, 90% of babies born will survive but usually have serious breathing issues. Ligaments form during this time, the nostrils open and the brain develops at a much faster rate. The retinas of the eyes are forming and baby can open them completely now. From this point forward, most of the development is in the lungs. By and large, all of the systems are developed and baby is working on gaining weight and developing immunities to survive outside the womb. At week 37, the pregnancy calendar is complete and gestation is considered full term - although the mother may carry the baby longer, an uncomplicated delivery is possible at this point.
On the other side of the womb, the mother may be going through a number of mental hoops as she and her partner contemplate parenting and how they will manage with all of the early learning tools they've already collected. Prenatal classes will be attended to ensure everyone knows what to do when the first signs of labor appear - breathing, relaxation, when to push, and whether to have pain medications are all part of the process. If the mother has taken good care over the course of her maternity, then she will likely feel confident about the birth and the health of the baby. However, even if she's done everything perfectly, there may be a challenge during labor or birth. Perhaps a c-section will be needed or baby may have to spend some time in the neonatal nursery if born too far before the due date.
By following the pregnancy week by week, having calculated the due date on the pregnancy calendar, a woman can now have a more intimate and informed time during these amazing months.