The amount of weight your infant gains starts slow and then begins to speed up near the end of pregnancy. A physician is concerned with the weight gain in the womb, and then again after the child is born. That is because their weight helps identify any possible problems. What mothers eat will directly reflect on the weight of the infant.

First Trimester

During the first trimester, your baby is just a mass of cells that does not weigh much of anything until at least eight weeks. This period is the most fragile for the fetus because it is very small and many things could go wrong.

If you smoke or drink, this is when you should stop so it will not affect the fetus’ growth, mental, or physical development. By the time you have reached the 12-week mark. Your infant is 45 grams, or one tenth of a pound, and almost four inches long.

Monthly Visits

After your first trimester has passed, you will visit the doctor every four weeks for a checkup. Your stomach will be measured, which helps the doctor determine if your infant is growing properly.

16 weeks – Your infant will be a third of a pound, or about 160 grams. He or she will be just over 6 3/4 inches. 20 weeks – Your infant
will be just over 3/4 of a pound, or 380 grams. He or she will be just over 8 3/4 inches. You should also be able to tell gender at this age.
24 weeks – Your infant will officially be over a pound, and will nearly be a foot long. While still very dangerous, making it to 26 weeks can result in a live birth with a long battle in the Neonatal Intensive Care Unit, NICU.
28 weeks – At the last of your monthly visits, your infant will be close to two and a half pounds and almost 14 inches long. Almost all births that occur after the 28th week result in live births. It does not mean that the infant is out of the clear however, and will usually spend a good six to ten weeks in the NICU.

Every Two Weeks

The four visits will be done every two weeks. You will have your sugar levels tested, as well as your infant’s growth. More emphasis is put on fetal development to make sure that he or she does not stop growing, or suddenly develop fetal distress. Your infant should gain about 3/4 of a pound every two weeks.

30 weeks – Your infant will be just over three pounds and a full 14 inches long. In some cases, infants are closer to 14 and a half inches long by this point in the pregnancy.
32 weeks – At 32 weeks, your infant is four pounds and almost 16 inches long. Babies born in this gestational week may require a week or two in the NICU, but not much more than that.
34 weeks – Your infant should start picking up speed on the weight gain and be about a full pound every two weeks. He or she will be five pounds and be almost 17 inches long. They should also flip into the head-down position and prepare for delivery.
36 weeks – This is the final “two-week” visit you will be making for your pregnancy. They switch to weekly, as you are officially full term at 36 weeks. Your infant will be six pounds and roughly 18 inches long.

End of the Pregnancy

Your infant will gain about a half pound a week, and a half an inch until delivery. Most women deliver between 39 and 42 weeks gestation. The average weight of an infant at birth is between seven and eight pounds. The average length of an infant is between 18 1/2 inches and 20 inches.

After Delivery

Once you deliver your baby, he or she will lose some weight initially. This does not mean there is anything wrong with your child, as long as it falls under the ten percent line. After that, the amount of weight gain will depend on whether or not your child is breastfed or formula fed. That is because breast milk digests completely and is not stored. The following rates are only rough estimates. Physicians prefer to look at where the infant is on the growth chart and that he or she remains very close to that percentile with no major changes.

Birth to Four Months – The first four months of life is when the infant will grow the most. He or she will experience growth spurts at 2, 4, 6, 8, 12, and 16 weeks. He or she should gain between five and eight ounces a week. If your child is eight pounds at birth, he or she should be at least 13 pounds in four months. As long as he or she is close to that, there is no reason to be concerned.

Four to Six Months – Weight gain will begin to slow and if you are nursing, you will notice immediately as the demand to nurse drops. Your infant should gain only three or four ounces a week. This means he or she will only put on about a pound a month for the next two months.

Six Months to One Year – For the remainder of the first year of life, the child will slow significantly on weight gain. He or she will gain, on average, two ounces a week. This is only a half-pound a month. This means that if your infant was eight pounds at birth, he or she may be right around 19 or 20 pounds.