The Netherlands Twin Register (NTR) began in 1987 with data collection in twins and their families, including families with newborn twins and triplets. Twenty-five years later, the NTR has collected at least one survey for 70,784 children, born after 1985. For the majority of twins, longitudinal data collection has been done by age-specific surveys. Shortly after giving birth, mothers receive a first survey with items on pregnancy and birth. At age 2, a survey on growth and achievement of milestones is sent. At ages 3, 7, 9/10, and 12 parents and teachers receive a series of surveys that are targeted at the development of emotional and behavior problems. From age 14 years onward, adolescent twins and their siblings report on their behavior problems, health, and lifestyle. When the twins are 18 years and older, parents are also invited to take part in survey studies. In sub-groups of different ages, in-depth phenotyping was done for IQ, electroencephalography , MRI, growth, hormones, neuropsychological assessments, and cardiovascular measures. DNA and biological samples have also been collected and large numbers of twin pairs and parents have been genotyped for zygosity by either micro-satellites or sets of short nucleotide polymorphisms and repeat polymorphisms in candidate genes. Subject recruitment and data collection is still ongoing and the longitudinal database is growing. Data collection by record linkage in the Netherlands is beginning and we expect these combined longitudinal data to provide increased insights into the genetic etiology of development of mental and physical health in children and adolescents.

The aim of this preliminary study was the estimation of renal blood flow in 16 premature newborns from twin pregnancies with mean body weight 1270 g and mean gestational age 29 weeks.

In control group we have 16 singleton newborns with mean gestational age 29 weeks and mean birth weight 1240 g. In both intervention and control group we have the similar clinical symptoms. The renal blood flow was carried out in the first day of life with the Acuson 128 XP Colour Doppler using the 6 and 7 MHz linear transducer. The renal blood flow parameters-PI, RI, Vmax, Vmin Vmean were measured in right and left renal arteries in theirs courses from the aorta to the renal hilus, by color sinal. In the investigation group the mean value of RI in right and left renal artery was 0,88. Mean PI in right vessel was 1,67 and in left 1,56. Mean V min in right and in left artery was 0,03 and mean V max in right artery was 0,34 and in left 0,33. Mean value of mean velocity in right vessels was 0,18 and in left 0,19.

In control group we observed in right artery mean value of PI 1,74 and in left 1,6. Mean RI was 0,86 and 0,86 in right vessel in left vessel. Mean V min was 0,05 in right and 0,04 in left artery. Mean V max was 0,37 in right and 0,34 in left artery. Mean value of V mean was 0,19 in right artery and 0,18 in left artery.

Using the student, Mann-Whitney and Shapiro-Wilk tests we have not observed statistically significant difference of Doppler parameters between control and investigation group and between the left and right artery. Although in newborns with broad PDA we noted significant higher value of RI (0,97, 0,98) than in newborns without PDA (0,78, 0,81).

The behavior of 120 full term and 160 preterm newborn twins was assessed in several key areas: Irritability, soothability, reactivity, reinforcement value, and activity level. Infants were assessed during various situations so that aggregate, or summary, scores representing each behavioral area could be obtained. Evaluations were made during a feeding period, an active sleep period, an awake alert period during which orienting and interactional behaviors were observed, a quiet period during which reactivity to stress was observed, and any fussy periods during which irritability and soothability were assessed. Significant within-twin-pair concordance of behavior was obtained for each of the areas of behavior, suggesting the influence of constitutional variables on neonatal behavior. Analysis of these data by sex resulted in significant within-pair concordance of behavior for same-sex but not for opposite-sex twins. The actual ratings on these behaviors differentiated between full term and preterm infants. Increased behavioral deviance was observed with increasing prematurity in the areas of soothability and activity level. The results are discussed in terms of increased risk factors for preterm twins.

Scores from a behavioral assessment of 160 stable preterm newborn twins were compared with those obtained from 120 full-term newborn twins. The twins were examined during various activities to obtain representative samples of behavior in the following behavioral categories: irritability, resistance to soothing, reactivity, reinforcement value, and activity level. Within-pair correlations were found in all of the behavioral categories, suggesting a constitutional influence on behavioral patterns during the neonatal period. The preterm infants demonstrated internal consistency of behavior similar to that of the full-term group in the first three categories. However, group differences were found when comparing the preterm with the full-term infants on actual ratings of the items. Behavioral differences between these full-term and preterm twins were comparable to those published for samples of singleton infants.