It can be difficult to calculate the exact date of conception although most women have their fertile period about 14 days after the first day of their last menstrual period. Because of this, doctors set an artificial but convenient time scale of 40 week calculate from the LMP, although a fetus actually reaches “full term,” meaning it is fully developed, after about 38 weeks.
Your Baby’s Progress
During this month your baby will usually shed almost all of the lanugo from his body. There may be some small patches left in odd places and perhaps some in his body creases.
His skin is smooth and soft, and there is still some vernix caseosa left on it (mostly on his back), which will help his passage down the birth canal. He may be almost chubby at birth. His fingernails are long and may have scratched his face; they will need to be trimmed after birth. He may be almost chubby at birth.
His fingernails are long and may have scratched his face; they will need to be trimmed after birth. His eyes are blue, although they may change in the weeks after birth; when he is awake they are open. In these last weeks, your baby produces increasing amounts of a hormone called cortisone from his adrenal glands. This helps his lungs to mature in readiness for his first breath.
His intestine is filled with a dark green, almost black substance called meconium. It is a mixture of the secretions from his alimentary glands, lanugo, pigment, and cells form the wall of his bowel. It will be the first bowel movement he will pass after birth (or he may pass it during delivery).
His own system is still immature, so to make up for this he receives antibodies from you via the placenta, which will protect him against anything for which you have antibodies, such as flu, mumps, and German measles. After he is born, he will continue to receive such antibodies through your breast milk.
His support system
The placenta now measures eight to ten inches (20-25cm) in diameter and is just over one inch (3cm) thick, thus creating a wide area for the exchange of nourishment and waste products between yourself and your baby. There are now more than two pints (1 litre) of water in the amniotic sac.
The hormones produced by the placenta are stimulating your breasts to swell and fill with milk. They also cause swelling in your baby’s breast, whether it is a boy or a girl, which will recede after birth. If your baby is a girl, the cessation of these same hormones following delivery may cause her to have light bleeding from her vagina (like a period) a few days after her birth.