Timing of screening tests and the subsequent risk of complications, in relation to gestational age at delivery.

<p>(A) Area under the receiver operating characteristic curve (AUROCC) for pre-eclampsia at different gestational ages in relation to uterine artery Doppler flow velocimetry performed at around 23 weeks gestational age. The origin of the <i>y</i>-axis is set to 0.5 as this is the value where the test is non-informative (data from <a href="http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.1001274#pmed.1001274-Yu1" target="_blank">[3]</a>). (B) Adjusted odds ratio for stillbirth at different gestational ages among women with maternal serum alpha fetoprotein levels in top 1% at 15–20 weeks. (C) As (B) except top 1% of maternal serum levels of human chorionic gonadotrophin (data from <a href="http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.1001274#pmed.1001274-Smith2" target="_blank">[13]</a>).</p

Researching New Methods of Screening for Adverse Pregnancy Outcome: Lessons from Pre-eclampsia

Researching New Methods of Screening for Adverse Pregnancy Outcome: Lessons from Pre-eclampsi

The effect of study design on sample size calculations and conclusions that can be drawn from screening studies.

<p>(A) Women are randomised to having or not having the screening test performed. (B) Women have the screening test performed and those who screen as high risk are randomised to having an intervention or having the result concealed. The number of women required (indicated in the top of each figure) is from a sample size calculation for 90% power to detect an effect at <i>p</i><0.05 (two sided). In panel (A), it is the number of women who need to be consented to be randomised to being screened or not screened and the calculation is based on the rate of the primary outcome comparing screened versus not-screened. In panel (B), it is the number of women who need to be screened and it is based on the rate of the primary outcome comparing intervention versus no intervention among women who screened positive. Both calculations assume an outcome with a background incidence of 1%, a screen positive rate of 5%, and a positive predictive value of 10% (hence a positive likelihood ratio of 11). Based on these parameters, the 95% of the population who screened negative would have a 0.53% incidence, giving a negative predictive value of 99.5% and a negative likelihood ratio of 0.52. The intervention is assumed to reduce the risk of the outcome by 60%. See <a href="http://www.plosmedicine.org/article/info:doi/10.1371/journal.pmed.1001274#pmed.1001274.s001" target="_blank">Table S1</a> for power calculations for both designs using other values of screening performance or intervention efficacy.</p

Logistic regression analysis of the association between previous abortion and the risk of preterm birth and neonatal death.

a<p>Adjusted for maternal height, age, history of miscarriage, marital status, socioeconomic status, and year of delivery.</p>b<p>Expressed as 0, 1, 2, and 3 or more.</p>c<p><i>p</i>-Value for trend.</p

Forest plots of odds ratios for preterm birth in Scotland by epoch.

<p>(A) Unadjusted odds ratio for a one-unit increase in number of previous abortions (coded as 0, 1, 2, and 3 or more) in relation to risk of preterm first birth among 732,719 women for births from 1980 to 2008. (B) As in (A), but odds ratio adjusted for maternal characteristics (deprivation category, previous miscarriage, maternal age, height, and marital status). (C) Adjusted odds ratio for a one-unit increase in number of previous abortions in relation to risk of preterm first birth among 414,373 women for births from 1992 to 2008. Odds ratios adjusted for maternal characteristics as in (B), but also for smoking. (D) Adjusted odds ratio for a 10-cm decrease in maternal height in relation to the risk of preterm first birth among 732,719 women for births from 1980 to 2008. Odds ratios adjusted for deprivation category, maternal age, marital status, previous abortion, and previous miscarriage. The interaction <i>p</i>-value is for a Wald test of the null hypothesis that the odds ratios did not significantly differ across the period 1980 to 2008. Year is treated as a continuous variable in all the statistical tests of interaction.</p

Crude rates of spontaneous preterm birth for nulliparous women with (<i>n</i> = 63,428) and without (<i>n</i> = 669,291) a past history of abortion in Scotland, 1980–2008.

<p>Crude rates of spontaneous preterm birth for nulliparous women with (<i>n</i> = 63,428) and without (<i>n</i> = 669,291) a past history of abortion in Scotland, 1980–2008.</p

Annual numbers of abortions by method among nulliparous women in Scotland, 1992–2008.

<p>These data were aggregated and were not linked to SMR02 data. (A) Observed data. (B) Sensitivity analysis where 5% of medical procedures are re-classified as surgical procedures with cervical pre-treatment. (C) Sensitivity analysis where 10% of medical procedures are re-classified as surgical procedures with cervical pre-treatment.</p

Cumulative incidence of preterm birth from 24 wk onwards in relation to number of previous abortions for 732,719 nulliparous women, Scotland 1980–2008.

<p>The relative risk of preterm birth for women with zero, one, two, or three or more previous abortions significantly varied across the range 24 to 36 wk gestational age (global test of proportional hazards assumption: <i>p</i> = 0.02). The graph is confined to the risk prior to 34 wk to allow better visualisation of the differences in incidence of extreme preterm births.</p

Maternal characteristics and outcomes in relation to the number of previous abortions.

<p>Data are <i>n</i> (percent) unless otherwise indicated.</p>a<p>Number (percent) missing data: height, 106,661 (14.6); marital status, 70,585 (9.6); smoking status (1992–2008), 43,998 (10.6).</p>b<p>Sub-group of births was used to calculate proportions: neonatal death data were available from 1985 onwards, and smoking data were available from 1992 onwards.</p><p>IQR, inter-quartile range.</p

Selection of the study cohorts.

<p>Selection of the study cohorts.</p