Summary -Vascular development and FETAL body composition during pregnancy- The effects of maternal adiposity (high body mass index - high BMI -), nutrient intake and storage (gestational weight gain - GWG -) and (abnormal) glucose tolerance (gestational diabetes - GDM - ) are regarded important cornerstones in metabolic research in pregnancy. In Chapter 1, I explained, that they play an important role in the development of complications in the mother and the fetus, both short- and long-term. I also reported on how the current state ofnbsp;in pregnancy has evolved and how it can be used for detailed studies of the unborn child. In this field of research, the fetal period is often conveniently summarized by its resultant birthweight. This outcome parameter is used to compare intra-uterine effects on long- and short term complications in epidemiologic studies. High and low birth weight has been linked to future increased cardiovascular risk profiles, fitting the nbsp;origin of diseases’ theory. Beside birth weight, more detailed information on the neonates’ body composition (fat distribution), in both lean- and fat mass might reflect the in utero development better, although fetal predictors for neonatal adiposity still have to be developed. Furthermore, there is no generally accepted definitionnbsp;‘neonatal BMI’ or neonatal adiposity. At present ponderal index or fat-mass percentage fill this lacuna. Finally, ultrasound in pregnancy is capable of obtaining information on the unborn child and uses an estimation for fetal weight. Accuracy for this estimate fluctuates around 6-12% of the actual fetal weight. In the obese mother, on the other hand, visualization of the fetus is even more limited. As stated in Chapternbsp;the environment in utero and in early neonatal life may induce a permanent response in the fetus and the newborn, leading to enhanced susceptibility to later diseases. Fetal overgrowth is related to a diabetic intra-uterine environment. The increased prevalence of diabetes mellitus (DM) in children of diabetic mothers is consistent with an epigenetic effect of hyperglycemia in pregnancy acting in addition to genetic factors that induce diabetes in next generations (human and animal data). Fetal growth restriction due to malnutrition on the other hand, leads to a higher incidence of CVD and type-2 DM in later life. Particularly when catch-up growth is present by high caloric postpartum intake. The third trimester seems to be a vulnerable period for the influence of maternal malnutrition, and hence fetal growth restriction (human and animal data). The role of environmental influences, such as excessive nutrition, nutritional restriction or low folic acid and vitamin B12 levels, on DNA methylation in early life development is called epigenetics. The effects of maternal and fetal nutrition stresses the importance of the embryonic environment on epigenetic imprinting for metabolic mechanisms on the future generations. Not every overweight newborn and not every newborn with intra-uterine growth restriction will develop problems in later life. Other factors of course influence final outcomes: in general it depends on the extent of adaptation and on its plasticity later on. In view from the fetus, the intra-uterine period has been associated with gender different intra-uterine physical adaptations to a changed nutrient supply from the mother. The male infant body composition has been shown to be more sensitive to maternal influences such as higher pre-gestational BMI and excessive gestational weight gain. And although gender is recognized as a determining factor for differences in outcome in adult medicine, little information is available on fetal gender influence in the prenatal period. Given these complexities the World Health Organization (WHO) Multicentre Growth Reference Study Group (MGRS) recommended GAMLSS (Generalized Additive Model Location, Scale and Shape) for the construction of (WHO) Growth Standards. In Chapter 3, we constructed fetal growth curves in a Caucasian population (12368 pregnancies) and furthernbsp;for fetal gender. The fetal head measurements were significantly larger in boys compared to girls from 20 weeks’ gestation onwards, equating to a 3 day difference at 20-24 weeks. Boys were significantly heavier, longer and had greater head circumference than girls at birth. The Apgar score at one minute and arterial cord pH were lower in boys. These longitudinal fetal growth curves for the first time allow integration with neonatal and pediatric WHO gender specific growth curves. Immediate birth outcomes are worse in boys than girls, and gender differences in intra uterine growth is sufficiently distinct to have a clinically important effect on fetal weight estimation and second trimester dating. Gender differences might play a role in obstetric or immediate neonatal viability management. The implication of these findings is that anbsp;and a girl at exactly 24weeks gestation might, based on the current late second trimester dating protocols with head measurements, be assigned a gestation as much as 3 days different and an estimated weight difference of 21gram at 24weeks favoring the boys; The term difference adds to 121gram, favoring the boys. Also the boys’ head circumference is larger (+0.6cm) at birth. In conclusion, the boys seem to be more vulnerable around viability age (22-24weeks), since they are estimated older than they are in reality. The girls are more vulnerable for this erroneous estimate at the latter, post-term period in pregnancy. Because at this stage, decisions on ending the pregnancy are often taken and they are older than estimated. But around term, boys do worse for the immediate start (lower first minute Apgar Score and cord-pH) compared to girls. In Chapter 4, a prospective cohort analysis was performed for the influence of maternal GWG and BMI on fetal growth. These factors influence independently fetal growth development during pregnancy and birth weight. Cluster analysis discerned four total GWG clusters: I: ≤0kg, II: 0-4kg, III: 4-12kg and IV: >12kg. For each cluster there was a different fetal weight evolution and also finally, different birth size. When cluster IV was compared to cluster I, the additive effect of the cluster difference on birth weight was +477g. The maternal BMI class acted independently on the fetal weight evolution. A higher BMI class increased fetal growth and hence birth weight. When BMI of 35 was compared to a BMI of 17, the additive effect on birth weight was +334g. The total GWG effect had most impact from 180 to 200 days gestation when there was a separation between the different GWG clusters. By identifying this relationship between GWG, growth and birth weight, we may now have time potential to influence weight gain during pregnancy and so possibly prevent perinatal complications, improve the metabolic and vascular traits of the infant and possibly improve outcomes in future pregnancies. Since birthweight is the resultant of the fetal period, the aim of Chapter 5, was to increase knowledge on the intra-uterine development with regard to fetal body composition. This was prospectively monitored in a highly controlled glucose tolerant cohort of 126 mothers. GWG was regarded ‘excessive’ (e-GWG) if the revised-2009 IOM upper thresholds were crossed. If not, the GWG was considered non excessive GWG (ne-GWG). In the prepregnant obese group, the fetal liver size (LL) and the abdominal fat thickness (AFT) growth trajectory increased significantly compared to normal weight women. E-GWG positively correlated with the growth in fetal abdominal circumference , LL, subscapular fat thickness (SFT) and AFT as compared to the ne-GWG group. Birth outcomes were significantly different for weight, length and head circumference in the e-GWG group as compared to the ne-GWG. Obesity and e-GWG both positively affect adiposity during fetal and neonatal life, with e-GWG clearly affecting fetal size in general, which was confirmed by birth anthropometry. In the normoglycemic pregnant women, determinants of the fetal trunk (LL, SFT, AFT and AC) are potentially useful in the prediction of neonatal adiposity. Our longitudinal study determined early signs of fetal adiposity associated with maternal obesity and particularly e-GWG in normoglycemic women. Maternal high BMI correlated with fetal liver size and abdominal fat, where e-GWG additionally correlated with increased subscapular fat and abdominal circumference development. Furthermore, fetal adiposity emerged asnbsp;reflection of a nutritious environment in utero with effects detectable as early as 20 weeks. Especially the indicators of the fetal trunk (liver-length, AFT, SFT and AC) are discriminative of fetal adiposity and warrant further investigation as potential early predictors of neonatal adiposity. Given these results we correlated in Chapter 6 these measurements in 121, highly controlled glucose tolerant mothers, prospectively, with neonatal body composition indices: neonatal fat mass (NFM), ponderal index (PI) and birthweight. The mean NFM at birth was 11.0% (SD±3.4%), with a cut-off of 15% for the 90th percentile (P90). No association was found between the maternal body mass index (BMI) and NFM. However, children born to mothers who had an e-GWG had a significantly higher NFM (11.6%) as compared to the ne-GWG mothers (10.4%). Fetal measures were highly correlated with neonatal measurements. Fetal abdominal circumference (AC), liver length (LL), subscapular- and abdominal fat thickness, humerus and femur fat mass development correlated significantly with 90th NFM percentile. Fetal AFT did not correlate with the PI. In the normoglycemic woman, e-GWG was associated with an increased neonatal adiposity. The neonatal PI and high adiposity (>P90 NFM) were preceded by an increased development of fetal central- and peripheral fat mass parameters. The fetal abdominal tissue development (AC, LL), reflecting fetal central adiposity, correlated highly to the 90th percentile of neonatal fat mass, showing their potential role as early predictors for neonatal fat deposition. In conclusion, the fetal fat measurements proved a high degree of correlation for neonatal adiposity, with a gestational age specific timing of first onset of aberrant fetal adiposity development: first (late first trimester) the abdominal circumference and fetal liver length, secondly (late second trimester) the truncal fat depositions of abdominal- and subscapular fat thickness and lastly (early third trimester) the peripheral fat depositions on the extremities (humerus and femur). The fetal abdominal fat development, a marker of fetal central fat deposition, correlated specifically to the 90th percentile of neonatal fat mass, for which further studies are needed to show its potential role as a more specific predictor for neonatal adiposity. Fetal developmental programming is influenced by maternal BMI, GWG and glucose intolerance. These factors affect the fetal growth and development, often conveniently summarized by its resultant ‘birthweight’. Birth weight is used in epidemiologicalnbsp;for as a proxy for long- and short term complications. Cardiovascular risks have been linked to birth weight, fitting the ‘fetal origin of diseases’ theory. Intima-media thickness (IMT) has been suggested as a marker of pre-clinical atherosclerosis. In the mother, IMT can be altered through dynamic circumstances related to pregnancy. In 38 low-risk pregnancies we investigated in Chapter 7, the feasibility of measurement of IMT at four pre-defined fetal and four pre-defined maternal arterial locations to determine vascular changes that could be associated with impaired vascular function throughout pregnancy. Fetal abdominal aorta IMT was measurable during the second trimester in 71% and during the third trimester in 100% of the cases, and umbilical artery IMT was measurable in 50% and 82% of cases during the second and third trimesters, respectively. Fetal IMT measurements were not possible during the first trimester. It was not often feasible to measure the IMT of the fetal common carotid artery, fetal renal artery and maternal iliac artery (maximal 20% of cases). Maternal common carotid artery, abdominal aorta and uterine artery IMTs were measurable throughout pregnancy. There was a significant relation between gestational age and IMT in the umbilical artery and a significant relation between body mass index and IMT in the maternal common carotid artery. IMT measurements are feasible in some maternal and fetal vessels of interest. Furthermore, fetal IMT development in abnormal pregnancy is of interest, as it could contribute to elucidating the mechanisms of intra-uterine fetal programming and the prediction of the origin of adult metabolic diseases. Pregnancy induces hemodynamic changes in women. The common carotid artery (CCA)nbsp;an easily accessible artery and is therefore often used in research (but also clinically) as representative for great artery health. Vascular changes in the CCA throughout normal pregnancy have not been elucidated before. In Chapter 8, we performed high resolution, radio-frequency (RF) ultrasound measurements of the CCA in 80 low risk mothers, prospectively, from first trimester onwards. All CCA properties and indices were significantly associated with gestational age in terms of decreasing compliance (Carotid Artery Compliance -CAC-) and increasing arterial stiffness (Young Elastic Modulus -YEM- and Stiffness Index -SI-). All indices (CAC, YEM and SI) were also significantly influenced by both maternal age and e-GWG, but when corrected for maternal age, the YEM remained positively correlated with GWG. Interestingly, no correlation was found with respect to pre-gestational BMI. In summary, our study provides to our knowledge the first longitudinal radio-frequency vascular data during pregnancy for the common carotid artery in low risk pregnant women. Whether the observed changes concern a transient, reversible phenomenon or represent a more durablenbsp;with correlates later in life requires further investigation. Particularly the long-term vascular effects of maternal weight gain during pregnancy as a risk factor for future cardiovascular disease. More challenging - when we look at our feasibility study reported in chapter 7 - is the research on the fetal abdominal aorta (fAA) development throughout pregnancy. In Chapter 9, we included seventy-four mothers in the final analysis. fAA measurements could reliably be obtained prospectively from 25 weeks onwards. All fAA properties (IMT, diameter (DIA) and distension (DIS)) showed a positive correlation with gestational age. FAA elasticity indices decreased during pregnancy with decreasing fAA Compliance (fAAC) and increasing arterial stiffness (YEM and SI). Elasticity indices (fAAC, YEM and SI) were also significantly influenced by fetal size. Interestingly, the fAA-IMT and DIS showed a significantly smaller increase in obese mother when compared to normal weight (≤24.9kg/m2 BMI) mothers, even after correction for fetal size. In conclusion, arterial stiffness in the fAA increases towards the end of gestation, and is more pronounced if fetal growth is fast. FAA-IMT development is negatively affected by high maternal BMI, suggesting a modulation of the fetal vessel-wall in the obese and overweight mothers. In summary, our study provides the first longitudinal radio-frequency vascular data during pregnancy for the fetal abdominal aorta in low risknbsp;women. We demonstrate a positive correlation of both fetal growth and maternal BMI with increased arterial remodeling during gestation in the fetal abdominal aorta. As with the results achieved with measures of the maternal CCA, whether this represents a transient or persistent phenomenon requires further investigation. Content Chapter 1. General aim, outline and introduction: 5 Chapter 2. Fetal growth and developmental programming: 27 Chapter 3. Sex differences in fetal growth and immediate birth outcomes in a low-risk Caucasian population: 39 Chapter 4. The influence of weight gain patterns in pregnancy on fetal growth using cluster analysis in an obese and non-obese population: 59 Chapter 5. Fetal central adiposity in utero is affected by both excessive gestational weight gain and obesity: a prospective cohort study in normoglycemic women: 75 Chapter 6. Neonatal adiposity is predicted by fetal central fat accumulation in utero, a prospective cohort study in normoglycemic women: 95 Chapter 7. Intima-Media Thickness measurements in the fetus and the mother during pregnancy: a feasibility study: 115 Chapter 8. Excessive gestational weight gain increases maternal common carotid artery stiffness in pregnancy: 133 Chapter 9. Fetal abdominal aorta remodelling correlates independent of fetal size and maternal obesity, a longitudinal study in utero: 151 Chapter 10. Summary and future perspectives: 169 Appendices List of abbreviations: 183 Abstract of Research: 187 Nederlandse Samenvatting: 191 Supplement: 209 Collaborators’ list: 231 Dankwoord: 239 CV & Publications: 243 nrpages: 254 status: published