After the sperm and egg combined, your newly created baby began a process of cell division that could rightly be called “explosive.” In these first four weeks, before some women even realize they are pregnant, your baby has begun to develop everything it needs to survive until birth. The fertilized egg will create your baby, the placenta, the amniotic sac and the amniotic fluid.
The creation of your baby begins before he is even attached to your uterine lining. As the egg divides and grows, cells begin to be specialized. Approximately 10 days after fertilization, your baby implants in the uterus. The lungs, heart and spinal cord begin to form. By the third week of life your baby’s heart is already pumping blood on its own.
By the end of the fourth week your baby is less than .03 oz, and is approximately 1/8 of an inch long.
When the egg becomes fertilized, your body begins producing higher levels of progesterone to prevent menstruation and keep the pregnancy healthy. It is initially produced by the ovary, but production will eventually be taken over by the placenta.
In response to the progesterone, the uterine lining thickens and the blood supply to the uterus increases. The cervix plugs with mucus to provide a protective barrier. Your uterus begins to enlarge and soften to allow implantation.
As your uterus begins to change, you may notice some pre-menstrual type cramping. The increased metabolic rate and the growth of the uterus cause an increased need to urinate. You will probably be more tired than usual and may even have short periods of faintness. The pregnancy hormones trigger the maturation process in the mammary glands, which may cause breast tenderness or soreness.
During this first month, you may wonder if you are pregnant. You can watch for the early signs of pregnancy and confirm your pregnancy with your midwife if you want to be sure.