What is length of pregnancy

She added it supports the suggestion that giving someone a "due date" may not be a great idea and can make women feel anxious when they go over. Women warned on iron 'overdose'. Human Reproduction. Royal College of Obstetricians and Gynaecologists. This is the first study to look at pregnancy this way. Tests for trend across quintiles were performed by scoring categories from 1 to 5, and by including the scores as a continuous variable in the models.

In multivariable analyses we adjusted for potentially confounding factors in three steps. In the third model, we additionally adjusted for cardiovascular risk factors of the mother prior to pregnancy; i. For fathers, we additionally conducted multivariable analyses of blood pressure, BMI, serum lipids and glucose with pregnancy length.

We evaluated the results of adjusting for intermediate factors that could lie on the causal pathway of the association between maternal height and pregnancy length or, alternatively; could be confounders. Induction of labour by medication or by caesarian section , and pregnancy complications were regarded as possible intermediate factors. To assess the role of induction, we restricted the main analyses to spontaneous onset of delivery excluding medically induced deliveries plus all elective caesarian sections plus acute caesarian sections before onset of labour.

Separately, we excluded pregnancy complications such as SGA offspring below the 2. We did linear regression analyses to assess associations between parental height and offspring birth weight in a similar way as was done for pregnancy length. This was done with the purpose of comparing associations between parental height and birth weight, with that of parental height and pregnancy length.

Possible effect modification by cardiovascular risk factors was also assessed in separate analyses. We included an interaction term between maternal height and the cardiovascular risk factor systolic blood pressure, BMI, glucose, lipids, pregestational metabolic and cardiovascular disease and a likelihood ratio test was used to compare the fit of models with and without the interaction term. Stata for Windows version The study was approved by the Norwegian Data Inspectorate, the Norwegian Board of Health, and by the Regional committee for medical research ethics.

All the participants of the study assigned an informed consent to participate in the HUNT 2 Study and also approved that data could be linked to the Medical Birth Registry of Norway. Mean maternal age at participation was Pregnancy length was associated with maternal age at delivery, maternal smoking and maternal systolic blood pressure, whereas no association with pregnancy length was found for parity, maternal educational status, maternal BMI, paternal BMI and paternal systolic blood pressure Table 1.

Table 2 describes pregnancy and offspring characteristics, stratified by quintiles of maternal height. Shorter maternal height was associated with lower mean birth weight, lower frequency of spontaneous onset of labour, and higher frequency of onset of labour by caesarian section elective and acute caesarian sections before onset of labour. Shorter women also had higher frequency of total number of caesarian sections, including acute caesarian sections after onset of labour.

Shorter women had higher rates of SGA offspring below the 2. Table 3 shows age-adjusted and multivariable adjusted differences in mean pregnancy length according to quintiles of maternal height. Additional adjustments for obstetric and socioeconomic measures maternal age at delivery, time between baseline at HUNT 2 and delivery, parity, offspring sex, maternal smoking, educational status, and receiving social benefits or not did not influence the effect estimates.

Neither did additional adjustment for levels of maternal cardiovascular risk factors prior to pregnancy systolic and diastolic blood pressure, BMI, concentration of glucose and lipids, hypertension, diabetes mellitus, kidney disease and coronary artery disease Table 3. Additional adjustment for paternal height did not change the results results not shown.

Table 4 shows age-adjusted and multivariable adjusted differences in pregnancy length according to quintiles of maternal height after restriction of the analysis to births with spontaneous onset of delivery. For deliveries with spontaneous onset, the difference in pregnancy length between the upper and lower maternal height group was reduced from 4.

Additional exclusion of pregnancy complications SGA, preeclampsia, and stillbirth did not substantially change these results results not shown. Paternal height showed no association with pregnancy length of the partner in age-adjusted and fully adjusted models Table 5. Neither did we find any association with pregnancy length for common paternal cardiovascular risk factors, including levels of blood pressure, BMI, serum lipids and glucose results not shown.

The risk was slightly increased after adjustment for obstetric factors, socioeconomic measures and cardiovascular risk factors prior to pregnancy. The risk of preterm delivery was lower in taller women when gestational length had been estimated by ultrasound, whereas only weak associations were observed when EDD was determined by LMP.

After restricting the analysis of maternal height with risks of pre- and post-term birth to deliveries with spontaneous onset Table 7 , the effect estimates were not substantially changed in relation to preterm births, but precision was lower due to the fewer numbers of pregnancies.

The associations with post-term delivery were slightly weaker for deliveries with spontaneous onset than for unselected deliveries. We found no association between paternal height and risks of pre- or post-term births Table 8.

Paternal height was, however, positively associated with z-score of fetal birth weight Table 9 , and the strength of the association among fathers was similar to the corresponding association for the mothers. In separate analyses, we assessed potential effect modification between maternal height and cardiovascular risk factors, but found no consistent evidence of any interaction all P-values above 0.

We found a positive association of maternal height with pregnancy length per se, and the effect was stronger when EDD was estimated by ultrasound than by LMP. Women with shorter stature had lower risk of post-term deliveries, and when EDD was based on ultrasound, they also had higher risk of preterm births. Paternal height and common cardiovascular risk factors of the father showed no association with length of pregnancy or with the risk of pre-and post-term births.

A Norwegian study among women with low risk pregnancies, spontaneous start of delivery, and EDD estimated by LMP found no association of maternal height with length of pregnancy [ 4 ]. We assessed paternal height and levels of paternal cardiovascular risk factors such as blood pressure, BMI, serum glucose and lipids, in relation to pregnancy length and risk of pre- and post-term birth. In contrast to previously reported associations between unfavorable cardiovascular risk factors among mothers and pregnancy length [ 14 ], no such associations were observed for the fathers.

Intergenerational studies have suggested that fathers may be of importance in determining pregnancy length in term and post-term pregnancies [ 2 , 18 , 19 ], but there has been little evidence for a paternal contribution to the risk of preterm birth [ 24 , 25 ]. In this study, paternal height was neither associated with pregnancy length nor with the risk of pre- and post-term birth. To our knowledge, these relations have not been reported previously.

In line with a recent review [ 26 ], however, we found a positive association of paternal height with offspring birth weight. The population based prospective design of the present study makes it unlikely that selection or recall bias can explain our findings.

Thus, the participants at fertile age in our study are likely to be representative for the source population. The relatively large sample size and the standardized measurements of height and other clinical measures in HUNT 2 ensure high precision of the effect estimates, and comprehensive information from self-administered questionnaires provides access to a range of possible confounders. By combining data from the HUNT 2 Study and the MBR it was possible to control for metabolic factors and other known risk factors on an individual basis.

A potential limitation in this study is that smoking status was sampled before rather than during pregnancy. This was due to lack of registration of smoking status in MBR until We performed sensitivity analyses restricted to pregnancies with available information on smoking during pregnancy from to , and the estimates did not differ substantially from the main results.

The MBR in Norway is a nationwide registry that includes information about virtually all births that have occurred in the country since Almost all pregnant women in Norway receive antenatal care, and hospital deliveries are free of charge, which minimizes any potential selection bias [ 21 ]. EDD was estimated by two different methods for most of the women ultrasound and last menstrual period , and the use of both methods was standardized throughout the study period.

The internal validity of our results is regarded as good. If shorter women have higher risk of hormonal disturbances with delayed ovulation, this could have biased our findings by underestimating EDD in LMP-based analyses. Often there is no known cause for a premature labour; however, some of the maternal risk factors may include: Drinking alcohol or smoking during pregnancy Low body weight prior to pregnancy Inadequate weight gain during pregnancy No prenatal care Emotional stress Placenta problems such as placenta praevia Various diseases such as diabetes and congestive heart failure Infections such as syphilis.

Overdue babies Around five out of every babies will be overdue, or more than 42 weeks gestation. Tests include: Monitoring the fetal heart rate Using a cardiotocograph machine Performing ultrasound scans. Some of the methods of induction include: Vaginal prostaglandin gel - to help dilate the cervix Amniotomy - breaking the waters, sometimes called an artificial rupture of membranes ARM Oxytocin - a synthetic form of this hormone is given intravenously to stimulate uterine contractions.

Where to get help Your doctor Your obstetrician Midwife or childbirth educator Things to remember The unborn baby spends around 38 weeks in the uterus, but the average length of pregnancy, or gestation, is counted at 40 weeks.

Since some women are unsure of the date of their last menstruation perhaps due to period irregularities , a baby is considered full term if its birth falls between 37 to 42 weeks of its estimated due date. More information here. Give feedback about this page. Was this page helpful? Yes No. View all healthy pregnancy. Related information. Support groups Victorian Infant Collaborative Study.

From other websites BirthNet. Content disclaimer Content on this website is provided for information purposes only. Reviewed on: Note: Content may be edited for style and length. Science News. Journal Reference : A.

Jukic, D. Baird, C. Weinberg, D. McConnaughey, A. Length of human pregnancy and contributors to its natural variation. Human Reproduction , DOI: ScienceDaily, 6 August Length of human pregnancies can vary naturally by as much as five weeks.

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