A baby’s weight after birth plays a pivotal role in his physical and mental development. Factors determining his birth weight include his gender, race of origin, the nutrition he received in his mother’s womb, his health at the time of birth and maternal health during pregnancy ^[1].

Average baby weight at birth

Full-term newborns (born at 38 to 40 weeks) usually weigh between 6 pounds (2.75 kg) and 9 pounds (4 kg) ^[1].

Newborn baby weight

During his stay at the hospital, a newborn’s weight is constantly monitored. It is essential for parents to make sure that their babies have about five to seven wet and three to four dirty diapers a day, as this indicates that he is getting the nutrition needed, which is pivotal in his weight gain.

Newborn weight loss

Newborns lose a certain percentage of their birth weight in the initial 5 to 7 days. Formula fed babies as well as breastfed infants shed 5% and 7% to 10% of their weight respectively ^[1,2]. The prime reason for this is the loss of the excess fluid they are born with ^[3]. Losing of birth weight in a newborn is not at all a matter of concern if they are passing urine and stool normally, until they lose more than 10% of the weight they had at birth ^[30].

How much weight should your newborn gain

After gaining back their lost birth weight in 10 to 14 days ^[4,27], most healthy newborns put on about half to one ounce of weight per day during the first month ^[29].

However, it may take more than three weeks to recover the lost pounds for babies who have undergone a significant reduction in weight post-birth ^[1], are sick or suffering from breastfeeding jaundice ^[23].

How fast do babies gain weight

If your baby is in good health, he should be gaining one to two pounds per month until the fifth or sixth month, after which he should have doubled his weight at birth ^[30,31]. By their first birthday, most of them weigh three times than what they were at birth ^[26].

Growth spurt: Infant weight gain

Growth spurt is a part of your baby’s developmental phase when he starts gaining weight at a faster rate than before ^[8]. It primarily occurs at 2 weeks, 3 weeks, 6 weeks, 3 months, 6 months and 9 months ^{[8, 9]}, lasting for a day or two in babies up to around three months and about a week in older ones ^[8]. During a growth spurt, your baby will feed for a longer time when nursed or remain hungry even after his bottle milk gets over ^{[8, 9]}.

Baby weight gain chart: Month by month

The chart given below is based on the growth standards devised by the World Health Organization (WHO), giving you an insight into how much your breastfed baby weighs in the first year of his life ^{[10, 11]}.

Months	Boys	Weight (pounds)3^rd to 97^th percentile
0		5.5 to 9.5
1	7.49 to 12.56	7 to 12
2	9.7 to 15.5	8.8 to 14.5
3	11.2 to 17.4	10 to 16.3
4	12.3 to 19	11.2 to 17.8
5	13.5 to 20	12 to 19
6	14 to 21.3	12.8 to 20.2
7	14.8 to 22.5	13.4 to 21
8	15.5 to 23	6.3 to 10
9	15.9 to 24	13.9 to 22.9
10	16.5 to 24.7	15 to 23.5
11	16.3 to 25.4	15.5 to 24.25
12	17 to 26	15.7 to 24.9

Girls	Months	Weight (pounds)3^rd to 97^th percentile
	0	5.2 to 9.25
	1	7 to 12
	2	8.8 to 14.5
	3	10 to 16.3
	4	11.2 to 17.8
	5	12 to 19
	6	12.8 to 20.2
	7	13.4 to 21
	8	6.3 to 10
	9	13.9 to 22.9
	10	15 to 23.5
	11	15.5 to 24.25
	12	15.7 to 24.9

Weight gain: Breastfed vs. Formula fed

It has been observed that formula-feds weigh more than breastfeeding infants, once they reach three to four months of age when both are almost twice their weight at birth ^[1]. This disparity in weight remains till their second birthday, after which the gap begins to bridge ^[5,7]. Studies have shown that by the time they reach their first birthday, nursing babies are thinner in comparison to formula-feds ^[6].

Why do breastfed babies gain less weight than formula-feds

The feeding pattern of nursing babies may be the probable cause of their slow weight gain throughout the first year of their life. Breastfed babies stop feeding on their own once they are full, whereas formula-feds are often made to finish off their bottle, thus getting a higher intake of food. Moreover, the protein composition of formula milk, different from breast milk, is believed to bring a change in the metabolism of the body ^[5].

Low birth weight in babies

Babies born full term may have a low birth weight due to certain genetic reasons. Other responsible factors might include being born to a teen mother or to parents with smaller body stature ^[28]. It can also occur in multiple pregnancies as the growing space in the uterus is shared by the babies ^[19]. Those with any congenital medical condition may also weigh less than normal at birth ^[28].

Premature baby weight

According to the World Health Organization (WHO), neonates delivered prior to 37 weeks are categorized as premature babies ^[12]. Taking into count their gestational age, they may have low birth weight (less than 5.51 pounds)^[19], very low birth weight (less than 3.30 pounds) ^[25]or extremely low birth weight (less than 3.30 pounds) ^[24]. Preterms born as early as 24 weeks may gain about .011 pounds (5 grams) a day while slightly bigger babies will experience an increase of approximately 0.44 pounds in their daily weight ^[13].

Babies not gaining weight

Your baby may not be gaining weight if he is not getting the required nutrition, having difficulty in digestion, not being able to get sufficient amount of breast or bottle milk because of some problem in his jaw, or even because of a serious medical condition ^[16]. It is advisable to monitor your baby’s weight on a regular basis to keep a check on his growth rate.

Failure to thrive

If the above-mentioned concerns persist for a prolonged period, your baby may grow at a slower rate in comparison to children of his age and gender ^[18] or lose weight at a faster pace, with the possibility of developing the problem of “failure to thrive” ^{[16, 17]}.

How to help your baby gain weight

Nursing your baby well is an important factor, influencing his weight gain. If you feel that your nursing baby is cranky or fussy even after latching onto your breasts for a longer time, speak to your pediatrician about the same as it might indicate that the amount of milk he is getting is not sufficient.
Introduce solids at the correct time as well as try giving him a nutritious diet of mashed or pureed fruits, vegetables, beans, egg yolks, boneless fish and other healthy foods to help him gain proper weight ^[20,22].
If your baby is old enough to eat finger foods, stay with him at mealtimes to make sure that he eats well rather than just nibbling at the contents on his plate.
Breastfed premature babies may be given a supplement known as human milk fortifier mixed in their feeds to help them cope up with additional requirements of protein, vitamins, calorie, calcium and iron ^[21].
Preemies who are formula fed may require Vitamin A, Vitamin C, Vitamin D and folic acid supplements ^[21].
References +

Baby Weight Gain