1 Estimating the Gestational Age and Pregnancy Trimester in the Niger Maternal Nutrition Project Rebecca R. Young, K. Ryan Wesse
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Estimating the Gestational Age and Pregnancy Trimester in the Niger Maternal Nutrition Project Rebecca R. Young, K. Ryan Wessells, Césaire T. Ouédraogo, Sonja Y. Hess Program in International and Community Nutrition, Department of Nutrition, University of California, Davis, CA, USA Corresponding authors: Rebecca R. Young ([email protected]) and K. Ryan Wessells ([email protected]) Study Overview The Niger Maternal Nutrition (NiMaNu) project is an implementation research project, using a quasi- experimental descriptive study design. Households with potentially eligible pregnant women from 85 randomly selected villages within the catchment area of 18 integrated health centers (CSI) were identified by employing a multi-stage clustered sampling design. Briefly, 18 CSI serving rural areas were selected by convenience sampling and randomized to the timing of participation. Within the catchment area of each CSI, 6-8 villages were randomly selected from each CSI. Participants were enrolled over a period of eighteen months through two community-based cross sectional surveys conducted at baseline and six months later after the implementation of a programmatic intervention (i.e. endline survey). The study was approved by the National Ethic Committee in Niamey (Niger) and the Institutional Review Board of the University of California, Davis (USA). Participants were asked to sign a written consent or fingerprint. The study was registered at www.ClinicalTrial.Gov as NCT01832688. Data Collection to Date Gestational Age Each study participant was interviewed and examined twice one month apart. Because ultrasound was not available and the majority of study participants were illiterate, several methods were used to date a woman’s gestational age. First, pregnant women were asked to estimate their last menstrual period (LMP) based on a time reference they were most familiar with. A woman could report her LMP by recalling the month and date of her LMP, by reporting the lunar position during her LMP and the number of lunar cycles since her LMP, and/or by reporting her LMP in proximity to a religious or cultural event. Women were also asked whether they had already felt the baby move and if that was the case, if they could estimate the time in months since quickening. Additionally, women were asked if 1 they were showing at the time of their first ANC visit. If a woman dropped out of the study before the second visit, it was recorded why she had dropped-out. Therefore, we knew if a woman gave birth to a live baby between the first visit and the scheduled time of the second visit. Symphysis-fundal height (SFH) was measured in duplicate on two occasions one month apart. During each physical exam, women were asked to empty their bladder and resume a supine position. SFH was measured from the symphysis pubis to the fundus uteri using a metric non-elastic tape (ShorrFlipTape©, Weigh and Measure LLC, Olney, MD)(1). The measurement was repeated and if the difference was >0.5 cm, a third measurement was repeated. Estimation of Gestational Age by Various Methods Based on the multitude of information provided by each woman, gestational age was estimated as follows: 1), the LMP was estimated based on the recall date, the lunar information and/or the local calendar. Using a lunar chart, the LMP was estimated, based on the phase of the moon during the last LMP and the number of moon cycles since the last LMP, and the phase of the moon at the time of the interview. If women remembered when their last LMP occurred in relationship to a major holiday (for instance, 2 weeks before a specific holiday), local holiday calendars were used to estimate the date of her last LMP. 2) Gestational age was assessed based on the number of weeks that had elapsed since the first quickening was felt. It was assumed that the first quickening was felt at 16 weeks gestation for multiparous women and 19 weeks gestation for primiparous women(2). 3) Fundal heights were measured in duplicate during two physical exams one month apart. The INTERGROWTH-21st equation for fundal height was then used to estimate gestational age(3). An extrapolation of gestational age was performed for fundal heights over 38 cm and under 20 cm. Accessing the Accuracy of the Gestational Age Estimations As these measurements were all estimations and prone to errors, a set of logic checks were used to estimate the reliability of each measurement. There were five logic checks: 1.) If quickening had not yet been felt it was assumed that the multiparous woman was less than 20 weeks pregnant, if quickening had not yet been felt it was assumed that the primiparous woman was less than 21 weeks pregnant. If quickening had been felt it was assumed that a multiparous women was more than 13 weeks pregnant and a primiparous women was more than 16 weeks pregnant. 2.) It was assumed that if a woman had 2 not yet started to show that she was less than 21 weeks pregnant and if she had started to show she was over 9 weeks pregnant. 3.) If the woman dropped out of the study before the second visit because she had given birth and that child was born alive, it was assumed that the baby’s gestation age was at least 27 weeks at time of birth. 4.) If SFH was available for both visits, SFH was considered acceptable, if the second SFH was not more than 12 cm greater than the first SFH or 6 cm less than the first SFH. 5.) It was assumed that no woman was less than 15 days pregnant and no woman was more than 43 weeks pregnant. Not all women had each estimate for gestational age, in fact no women had all six measurements. Additionally, the logic checks filtered away many gestational age estimates that were not possible. If any gestational age measurement did not pass a logic check, it was excluded. For example if gestational age as measured by the lunar cycle calculated a woman to be 20 weeks in gestation at the first visit, but she had given live birth less than 1 month later, than it was assumed that the lunar cycle gestational age estimate was incorrect. Creating a Weighted Average of Gestational Age The overall gestational age estimation was calculated as a weighted average. The weighted average was based on two factors: 1.) the percentage of time that each measurement passed the logic checks (which ranged from 70-90%) and 2.) an assigned importance measurement. It was determined that the self- reported methods of gestational age estimation (reported date, lunar cycle and proximity to a holiday) together counted for 1/3rd of the total score, the two SFH together accounted for 1/3rd of the score and the time of first quickening counted for 1/3rd of the score. The weighted average was calculated in such a way that if a measurement was missing (due to either missing information or a failed logic check), the other values would compensate for this missing value. If there was only one known measurement, then the gestational age was estimated based solely on that measurement. References 1. Engstrom JL, Chen EH (1984) Prediction of birthweight by the use of extrauterine measurements during labor. Res Nurs Health 7, 315-323. 2. Levene M, Tudehope D, Thearle M (2000) Essentials in Neonatal Medicine: Wiley. 3 3. Papageorghiou A, Ohuma E, Gravett M et al. (2016) International standards for symphysis-fundal height based on serial measurements from the Fetal Growth Longitudinal Study of the INTERGROWTH- 21st Project: prospective cohort study in eight countries. Br Med J 355, i5662. 4 .