A comparison of pregnancy dating methods commonly used in South Africa: A prospective study (original) (raw)

2013, South African Medical Journal

Optimal management of pregnancy relies on accurate assessment of the gestational age (GA) of the fetus; which can be determined by the history of the last menstrual period (LMP), clinical estimation of the 1st symphysis-to-fundal height measurement (FH) or ultrasonographic fetal biometry. However, many women fail to recall their LMP accurately. [1] Moreover, pregnancy duration and fertile period are highly variable, even for women with regular cycles. [1] FH suffers from poor reproducibility and high variability due to maternal and fetal factors; [2-4] its accuracy for dating has not been extensively studied [5-7] and requires FH dating charts (rather than growth charts). Ultrasonography (US) in the 1st, or early 2nd trimester, is highly reproducible [8] and widely used for dating, since early biological variability of fetal biometry is minimal. [9] In the past, certain LMP was used for dating as long as the GA was within 7, 10 or 14 days of the estimate of GA by US, [10] but now 1st, or 2nd trimester, US is increasingly recommended as the single dating method because of its smaller error rate. [1,11,12] The accuracy of dating GA by US in late pregnancy is less well studied, but may be clinically valuable. [13,14] The current policy in the Western Cape Province of South Africa (SA) provides for a routine US examination between 18-23 weeks of the clinically estimated GA for low-risk pregnancies since this reduces the number of presumptive post-and pre-term deliveries as well as the number of referrals to a higher level of care for suspected deviations in fetal growth. [15] The approximately 34% of women who typically present at >23 weeks [16] do not routinely receive US. Pregnancy dating is based on a pragmatic guideline incorporating information from the LMP, FH and early US (if available). [17] The accuracy of this guideline and the clinical value of late US-based GA dating have not been assessed. Our aim was to determine the accuracy of the different dating methods, and of their combinations, since they are currently widely used in SA. We performed a prospective study that compared the current US policy with a policy that included a routine booking scan. Objectives (i) Determine the accuracy of US in predicting the actual date of delivery (ADD), (ii) compare the incidence of GA-related outcomes and (iii) assess the influence of clinical variables on discrepancies between the dating methods. Methods The main study, described elsewhere, [16] was a prospective, interventional, before-and-after study in low-risk women (n=750 in each study arm) initiating antenatal care in 2 midwife-led clinics in the Metro East region, Cape Town, Western Cape. The study was approved by the Committee for Human Research, University of Stellenbosch (project no. N07/04/080) and a waiver of individual informed consent was granted. During the 1st period (October 2007-January 2008, comprising the control group), women received a routine US at 18-23 weeks GA, determined by clinical estimation based on a combination of the date of the LMP and FH. Additional scans were permitted, as per current policy, only for specified clinical indications. During the 2nd period, (February-April 2008, comprising the study group), a 'booking US scan' was obtained for all women within 7 days of their booking, regardless of GA. Singleton pregnancies continuing to >24 weeks were included if information was available for ≥1 dating method if ADD was known and ≥2 if ADD was not. We excluded pregnancies A comparison of pregnancy dating methods commonly used in South Africa: A prospective study