For convenience in calculating, pregnancy or gestational period is divided into 3 trimesters, each lasting  3 months.  But, changes occur in the growing fetus on a weekly basis and the internet is full of resources as well as pregnancy pictures of the various changes that take place in both mother and fetus on a daily or weekly basis. Mothers-to-be can track their own fetal development and make comparisons with  other expecting mothers’  and their own changes, and this makes pregnancy more transparent and also takes away the feeling of uncertainty and mystery that invariably accompanies pregnancy. Given below is a brief overview of changes that occur in the fetus on a monthly basis.

First month- The first step in pregnancy is fertilization of the egg by the sperm. The gender  of the fetus is finalized at this stage. The fertilized egg then gets implanted on the wall of the uterus, which is called the endometrium and which provides nourishment to the embryo. The embryo develops the yolk sac and the amnion. The former provides nutrition to the embryo and the latter, which is a fluid –filled sac protects the embryo from mechanical shocks.

Second month-This stage is characterized by the formation of the brain and the spinal cord respectively. The placenta also develops and it is through this maternal tissue that nutrients and oxygen are passed on to the embryo from the mother. At this stage, the embryo measures about 0.08 inches to 0.2 inches. The brain and nervous system begin to develop as also the respiratory and the digestive system and the heart beat can be detected by an ultrasound scan. The umbilical cord which forms a bridge between the mother and the baby develops at this stage and the growth of digestive organs and lungs continue. Facial features slowly become distinct and growth of arms, fingers, toes, eyes and the genitals  begins.

Third Month-By this time, most of the vital organs have been formed, and the tooth buds appear. From the 11th week to the 20th week, rapid growth occurs. Gender  differentiation becomes possible around the 14th week. Blood circulation between the uterus and the fetus begins and placenta becomes fully functional.
Fourth Month-The baby’s kidneys begin to function and muscular movements of the digestive system begins to appear. Hand starts functioning and the face takes on a more human appearance.

Fifth Month-Growth of various organs continues. Eyebrows and hair appear. Muscular movements are quite pronounced and the baby may even start sucking its thumb.
Sixth Month- Bones become heavier and the baby may now weigh approximately 3.9 ounces. The ear bones and nerves of the brain have developed at this stage and the baby can hear the mother’s heart beat. The fetus grows and occupies a large part of the uterus.

Seventh Month-The baby weighs at least two pounds and measures around nine inches.  Lungs develop air sacs and start expanding with the breathing. The auditory and visual systems begin to develop in the brain.

Eighth Month- At this stage,  the baby looks a lot like what it would look at the time of its birth, except smaller and thinner. The immune system develops and if the baby has a premature birth now, there is a good chance of its survival.

Ninth Month- The baby weighs about 6 pounds and continues to grow, reaching about 7 pounds at the time of delivery. Its length measures about 21 inches long, and the baby attains maximum brain growth at this stage. The skin color changes from red to pink. The baby is ready for delivery any time now and the doctor can predict if it is going to be a normal or breech presentation.