the baby's parents' height and stature. if the baby is a boy (baby boys tend to be larger than baby girls) having older siblings (the chance of fetal macrosomia increases with each pregnancy)
This study suggests that during development in the womb, boys are more responsive to the mother's immediate diet than are girls. If the nutritional needs are adequate, boys grow big and weigh more at birth on average than girls.
Male babies generally grow faster and bigger than females. This occurs in both the animal and human worlds, but until now we haven't really understood how or why.”
Physical size and growth
Right from the start, boys tend to weigh more at birth and this trend continues as babies age, with girls measuring about a half pound less. But girls catch right up as the toddler years approach. Most of them reach half their adult height by 19 months of age.
Although it is widely known that boys are slightly larger than girls in the first trimester and at birth, there has been no consideration of fetal gender in the development and interpretation of fetal growth curves [5,6,7,8].
It is true that on average baby boys weigh more at birth than baby girls, and so this could make the bump for a boy slightly bigger. But this small difference in weight does not change the shape of the bump.
The truth is, the sex of your baby doesn't have anything to do with the appearance of your pregnant belly. The belly test to guess a baby's gender is simply an old wives' tale that has been passed down through the years.
Worldwide, boys are heavier than girls at term birth. This difference is thought to be generated by androgen action [2], but its time course during fetal life is unknown.
At birth, boys tend to be longer than girls at any placental weight. Boy's placentas may therefore be more efficient than girls, but may have less reserve capacity. In the womb boys grow faster than girls and are therefore at greater risk of becoming undernourished.
Research shows girls kick as often as boys. Babies who kick a lot in the womb are also more active after birth.
Male births were much more likely to require the use of oxytocin, a hormone which stimulates contractions. "Of the women carrying male infants, 70 per cent of them had completely normal deliveries, compared to 76 per cent of females."
A father's genetic code influences the weight of a baby at birth, according to a new study led by the UCL Institute of Child Health (ICH).
Investigators at Lenox Hill Hospital, in partnership with Sweden's Karolinska Institute, recently found that, on average, males spent about one day longer in the womb than females.
Other Factors
For example, male infants tend to weigh slightly more at birth than female infants. 17 First babies tend to weigh less than subsequent babies27 and twins and other multiples are usually smaller than singletons.
Nature is designed to favour the conception of boys from September to November and girls from March to May because of an evolutionary mechanism aimed at keeping the overall sex ratio as near to 50:50 as possible, the scientists said.
Or that if you feel your baby moving more on the right side, then you're probably having a boy. But there's no evidence that there's a difference between the movements of boys and girls in the womb (Medina et al 2003).
When we look at the statistics the chances of having a boy or a girl are almost the same and there's no medical evidence to suggest we can influence this. You may, however, have heard about the 'Shettles Method'. In the 1970s Dr Shettles found that female and male sperm had different characteristics.
The truth is your baby's sex has very little to do with the length of pregnancy.
Genetic factors and maternal conditions such as obesity or diabetes can cause fetal macrosomia. Rarely, a baby might have a medical condition that makes him or her grow faster and larger. Sometimes it's unknown what causes a baby to be larger than average.
The sex of the child has no influence on the length of the pregnancy. This is influenced by the birth order, the propensity to smoke (tobacco), the mother's weight gain in pregnancy and her social level.
The mother's height and weight impact the weight of the baby at birth - and the father's height and weight have an impact too. Some babies are small because it runs in the family. However, some babies may take more after the mother or the father, rather than being an average of both.
Women carrying a male fetus have significantly increased maternal weight gain during pregnancy when compared to women with a female fetus. The increased sex ratio remains when adjusting for each newborn weight group.
The Bottom Line
The two sex chromosomes in the egg and sperm are what determine whether you'll have a boy or girl. Eggs always have an X chromosome, and sperm have either an X or Y chromosome. Whichever sperm is the winner will penetrate and fertilize the egg, creating either an XX (girl) or XY (boy) pair.
The way you carry has everything to do with the tone of your abdominal muscles, body shape, and a few other factors. The general size and shape of your belly don't have much to do with your baby, their health, or their size. A healthy baby can grow regardless of how your belly looks.