**2. Relationship between the parental BMI and the anthropometric development of the fetus**

Most of the studies conducted are based on the relationship of birth weight as an important anthropometric parameter and its measure of the fetal growth and development [16]. Ay et al., for the first time examined the relationship of maternal anthropometrics with the fetal growth and development at various stages of pregnancy through a large cohort study [2]. They showed that maternal pre-pregnancy BMI (pre-BMI) gestational weight and height has an influence on the fetal growth and development starting from mid-pregnancy onward [2]. These maternal parameters can be associated with the small and large size of the infants and are related to an increasing gestational age. The findings of the study were independent of the social factors such as the socio-economic condition and lifestyle of the mother [2]. Studies pertaining to the timing of the anthropometric development of the fetus have been focused mainly on the birth weight and fetal growth. However, third trimester studies till date remains inconclusive [6, 17–20].

Factors such as diabetes or insulin resistance have a strong effect on the high maternal prepregnancy BMI and weight gain and can lead to increased fetal glucose and an increased birth weight along with a risk of cardio-metabolic disorder [20]. Maternal nutritional status is also an important criterion that can be strongly associated with the pre-pregnancy BMI and the outcome of the fetal weight [21]. However, further studies are important to prove this exclusively including the maternal anthropometric mechanisms which affect the fetal growth [2].

A low birth weight of a neonate can be linked to impaired overall growth and development of the baby and overweight can be related to severe complications of the child during delivery [3]. Fetal and offspring overweight can also be related to obesity in children in later life [3, 4].

Apart from the weight of the neonate, factors such as the maternal height, weight, and metabolic rate are also important anthropometric parameters related to the growth and development of the fetus [5]. Small and selected studies have suggested that pre-pregnancy pre-BMI and weight during the gestation period of the mother are important factors that predict the

Normally it is gestational weight, which is indicative of both nutritional status and tissue development, whereas pre-pregnancy BMI only reflects the nutritional status [12]. However, the relationship between the two is still not clearly established including that of the maternal BMI and other anthropometric parameters related to the fetal growth and development in pregnancy [2]. An early pioneering study in Calcutta led by Prof. K.L.Mukherjee involving anthropometric measures of the aborted human fetus collected ethically from all the trimesters was conducted [13]. They found the weight of the liver decreased with increase in gestational period, whereas organs such as lungs increased in their size with increase in the gestational period [13, 14]. The adrenal glands in the first-trimester remain larger than the kidneys; however, after 12 weeks

The group was unable to detect any thymus tissue at 8 weeks of gestation in smaller fetuses. However, they could detect the presence of the thymus gland in larger fetuses weighing more than 5 g between the first and second trimester period. In 28 week old fetuses, the thymus could be easily detected indicating that with an increase in the gestational week, the thymus becomes observable because of its increase in weight and size [15]. In case of sexual organs, the growth and development of the tests were not uniform. However, a trend was observed where there was a decrease in the weight of the testes with an increase in the gestational period in the male fetuses and a similar pattern was also observed in case of the ovaries in female fetuses [13].

**2. Relationship between the parental BMI and the anthropometric** 

Most of the studies conducted are based on the relationship of birth weight as an important anthropometric parameter and its measure of the fetal growth and development [16]. Ay et al., for the first time examined the relationship of maternal anthropometrics with the fetal growth and development at various stages of pregnancy through a large cohort study [2]. They showed that maternal pre-pregnancy BMI (pre-BMI) gestational weight and height has an influence on the fetal growth and development starting from mid-pregnancy onward [2]. These maternal parameters can be associated with the small and large size of the infants and are related to an increasing gestational age. The findings of the study were independent of the social factors such as the socio-economic condition and lifestyle of the mother [2]. Studies pertaining to the timing of the anthropometric development of the fetus have been focused mainly on the birth weight and fetal growth. However, third trimester studies till date remains inconclusive [6, 17–20]. Factors such as diabetes or insulin resistance have a strong effect on the high maternal prepregnancy BMI and weight gain and can lead to increased fetal glucose and an increased birth

outcome of the fetal weight and its development [6–11].

12 Body-mass Index and Health

of gestation the kidney outweighs the adrenal gland.

**development of the fetus**

Another important study was conducted in Pune to find out the relationship of BMI and height on 557 pregnancies with fetal age between 17 and 29 weeks of gestation and observed through ultrasound method. The group reported that parental height was positively associated with an increase in the fetal head circumference and femur length [22]. In case of higher BMI rates in mothers, ultrasound images showed that the fetus in utero had a smaller head circumference at 17 weeks and it increased during the time of birth. In mothers having lower BMI rates, head to fetal body ratio was observed to be large at 17 weeks. The placental volume was also depended on the maternal BMI and the paternal height [22].

As mentioned before, pre-pregnancy BMI is an important parameter and marker for nutrition, energy, and tissue development [22]. In the above study, further, the group of clinicians found a positive correlation between the paternal height and placental volume at around 17 weeks of fetal development although the direct role of maternal BMI on the 17 weeks fetus was found to negative [22]. Better maternal nutrition is thought to provide the mother with a higher BMI, which helps in the placental development in early pregnancy resulting in greater fetal development in the final gestational phases [23]. Similarly like Goldberg et al., the study further found a positive relationship with head circumference growth in the 29 weeks to birth interval [24].

A study by Tahergorabi et al., showed a weak association of maternal BMI with respect to the sex of the first-trimester fetus [25]. They showed maternal BMI was related to the female fetus rather than the male fetus and maybe sex-dependent in nature [25]. Other factors that can influence the impact of maternal BMI on birth weight of the fetus include maternal age, ethnicity, gestational diabetes mellitus and insulin resistance, education and environmental factors, and hypertension including genetics [26, 27].

Until recently the relationship of BMI and its significant influence on the developing fetus was unknown. Studies and observations have come to acknowledge the fact that maternal weight, BMI including that of the fetus plays an important role in determining the fetal growth and development [2, 28–30].

Recently, the significance of paternal BMI and dietary behavior in animal studies have also shed light into the fact that paternal obesity including BMI can affect the offspring in a gender-dependent manner [31]. Chen et al., in one such pioneer study observed that paternal BMI during the time of conception can be sex dependent and can influence the male but not the female fetus through mechanisms hitherto unknown [31]. However, the above cannot be exclusively confirmed as of yet due to very few studies relating to paternal BMI and its relationship with the fetal development [32].
