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Table 2 Case definition and sample size for pregnancy and perinatal outcomes across participating studies

From: Integrating multiple lines of evidence to assess the effects of maternal BMI on pregnancy and perinatal outcomes

Outcomes

Case definition

N

N cases

% cases

Binary outcomes

 Miscarriagea

Self-reported in index pregnancy

91,757

107

0.12%

Self-reported in previous pregnancies

376,434

70,181

15.71%

 Stillbirtha

Self-reported in index pregnancy

91,942

292

0.32%

Self-reported in previous pregnancies

174,440

4613

2.58%

 Hypertensive disorders of pregnancy

Gestational hypertension or preeclampsiab

416,803

26,867

6.06%

 Gestational hypertension

Elevated blood pressure without proteinuriab

406,103

17,607

4.16%

 Preeclampsia

Elevated blood pressure with proteinuriab

401,184

9827

2.39%

 Gestational diabetes

Hyperglycaemia first diagnosed in pregnancyc

446,526

14,338

3.11%

 Maternal anaemia

Maternal anaemia during pregnancy defined as Hb < 110 g/L (1st trimester) or Hb < 105 g/L(2nd or 3rd trimesters)

92,002

2425

2.57%

 Perinatal depression

Self-reported diagnosis or assessed depression symptom scales

113,614

9320

7.58%

 Pre-labour rupture of membranes*

Membrane rupture before the onset of contractions

249,265

19,339

7.20%

 Induction of labour*

Labour needed induction

114,075

17,351

13.20%

 Caesarean section*

Delivery by caesarean section

204,093

27,967

12.05%

 Preterm birth*

Gestational age at birth < 37 weeks

261,473

14,090

5.11%

 Large-for-gestational age*

 > 90th percentile for z-score of birthweight accounting for sex and gestational aged

118,667

12,386

9.45%

 Small-for-gestational age*

 < 10th percentile for z-score of birthweight accounting for sex and gestational aged

118,667

8958

7.02%

 Low birthweight*

Birthweight < 2500 g

247,716

14,964

5.70%

 High birthweight*

Birthweight ≥ 4000 g

239,460

8142

3.29%

 Low Apgar score at 1 min*

Apgar score at 1 min < 7

98,868

5760

5.51%

 Low Apgar score at 5 min*

Apgar score at 5 min < 7

99,434

1167

1.16%

 Neonatal intensive care unit (NICU) admission*

Neonate admitted to NICU

93,522

8262

8.12%

 Breastfeeding initiation*

Ever breastfed

94,116

78,472

45.47%

Continuous outcomes

 Birthweight*

NA

326,537

NA

NA

 Birth length*

NA

95,649

NA

NA

 Ponderal index at birth*

NA

95,562

NA

NA

 Gestational age at birth*

NA

118,723

NA

NA

  1. Detailed information on each of the outcomes in each cohort is provided in Additional file 1: Supplementary material and Additional file 2: Supplementary table 1
  2. aMiscarriage and stillbirths in the index pregnancy were used in multivariable regression and paternal negative control analyses, while miscarriage and stillbirth reported in previous pregnancies were used in Mendelian randomisation analysis
  3. bWhere possible, we applied the International Society for the Study of Hypertension in Pregnancy criteria (ISSHP), which defines any HDP as SBP ≥ 140 mmHg or DBP ≥ 90 mmHg, measured on two occasions after 20 weeks’ gestation, with those who are then defined as having pre-eclampsia also having proteinuria (with the raised blood pressure) of at least 30 g/Dl and those defined as having gestational hypertension being those who do not meet criteria for pre-eclampsia. By contrast, in some studies (e.g. UK Biobank), information on diagnosis was extracted directly from medical records
  4. cCriteria used to define hyperglycaemia first diagnosed in pregnancy varies across studies. Most studies obtained information from questionnaires (i.e. self-reported diagnosis) or from medical records [ICD-10 code O24]
  5. dDifferent reference populations were used to calculate percentiles across studies
  6. *For these a priori selected outcomes, additional Mendelian randomisation analyses were conducted accounting for offspring genotype
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BMC Medicine

ISSN: 1741-7015

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