Study reference

Study characteristics

Patient characteristics ²

Intervention (I)

Comparison / control (C) ³

Follow-up

Outcome measures and effect size ⁴

Comments

Algeri, 2019

Type of study:

retrospective observational study

Setting and country: one hospital between January 2000 and July 2017, Italy.

Funding and conflicts of interest:

Funding was not reported in the article.

No potential conflict of interest was reported by the authors.

Inclusion criteria:

-diamniotic pregnancy

-vaginal delivery of the first twin

Exclusion criteria

-higher twin order

-monoamniotic pregnancies

-cesarean delivery of the first twin

-patients with missing data

N total at baseline:

n=400 diamniotic twin pregnancies

Intervention: ≤ 30 min, n=365 twin pregnancies

Control: >30 min, n=35 twin pregnancies

Important prognostic factors²:

Maternal age ± SD:

I:32.8 ± 4.6

C: 34.24 ± 6.30

P=.1

Monochorionic pregnancy, n(%)

I: 110 (30.1%)

C: 5 (14.3%)

P=.051

Gestational age at birth ± SD

I: 36.1 ± 2.5

C: 36.1 ± 3.3

P=.964

Nulliparity, n(%)

I: 158 (43.3%)

C: 18 (51.4%)

P=1.0

Infertility treatment, n(%)

I: 51 (14.0%)

C: 7 (20.0%)

P=.32

Groups comparable at baseline?

Monochorionicity was more frequent in case

of shorter intertwin delivery interval (30.1 versus 14.3%, p=.05)

intertwin delivery interval (defined as time elapsed between the delivery of first and second twin): ≤ 30 minutes

Dichorionic diamniotic uncomplicated pregnancies are delivered at 38–39 weeks in this hospital. They do not consider a predefined interval cut-off to expedite delivery if maternal and second twin healthy conditions are maintained.

intertwin delivery interval (defined as time elapsed between the delivery of first and second twin): > 30 minutes

Length of follow-up:

Not reported

Loss-to-follow-up:

Not reported

Incomplete outcome data:

Not reported

Outcomes reported for the 2^nd twin.

Mode of delivery 2^nd twin, n(%)

P<.001

Vaginal delivery

I: 333/365 (91.23%)

C: 18/35 (51.43%)

Vacuum delivery

I: 20/365 (5.48%)

C: 7/35 (20.00%)

Emergency cesarean section

I: 12/365 (3.29%)

C: 10/35 (28.57%)

Apgar score<5, n(%)

(not further defined)

I: 8/365 (2.2%)

C: 0/35 (0%)

P=n.a.

pH ≤7.00, n(%)

I: 5/365 (1.37%)

C: 2/35 (5.71%)

P=.11

pH ≤7.10, n(%)

I: 14/365 (3.84%)

C: 3/35 (8.57%)

P=.17

Jaundice, n(%)

(diagnosed using ICD-9 codes)

I: 58/365 (15.89%)

C: 7/35 (20%)

P=.633

Sepsis, n(%)

(diagnosed using ICD-9 codes)

I: 3/365 (0.82%)

C: 0/35 (0%)

P=n.a.

Neonatal enterocolitis, n(%)

(diagnosed using ICD-9 codes)

I: 0/365 (0%)

C: 0/35 (0%)

P=n.a.

Postpartum hemorrhage, n(%)

Defined as an amount of bleeding that exceeds 500 mL following vaginal delivery or 1000 mL following caesarean delivery

I: 82/365 (22.5%)

C: 12/35 (34.3%)

P=.523

Postpartum hemorrhage >1500 mL, n(%)

I: 9/365 (2.5%)

C: 1/35 (2.9%)

P=1.0

Breech presentation of the 2^nd twin, n (%)

I: 69/365 (18.9%)

C: 2/35 (5.71%)

P=.62

Cukierman, 2019

Type of study: retrospective cohort study

Setting and country: a tertiary

hospital between January 2011 and September 2017, Australia

Funding and conflicts of interest:

Funding was not reported in the article. None of authors declare a conflict of interest.

Inclusion criteria:

Twin pregnancies with a vaginal delivery of the first twin after 24 weeks

gestation.

Exclusion criteria:

-an elective caesarean section or caesarean section of the first twin were excluded.

-major congenital abnormalities in either twin

N total at baseline:

Intervention: ≤ 30 min, n=317 twin pregnancies

Control: >30 min, n=28 twin pregnancies

Intervention: ≤ 10 min, n=164 twin pregnancies

Control: >10 min, n=181 twin pregnancies

Important prognostic factors²:

Maternal age ± SD:

I_{≤30 min}: 30.9 ± 5.2

C: 31.2 ± 5.4

P=0.78

I_{≤10 min}: 31.1 ± 4.8

C: 30.8 ± 5.5

P=0.58

Monochorionic, n (%)

I_{≤30 min}: 99 (31.2%)

C: 3 (10.7%)

p=0.02

I_{≤10 min}: 59 (36.0%)

C: 43 (23.8%)

p=0.01

Dichorionic, n (%)

I_{≤30 min}: 218 (68.8%)

C: 25 (89.3%)

I_{≤10 min}: 105 (64.0%)

C: 138 (76.2%)

Gestational age,

weeks, median (IQR)

I_{≤30 min}: 36.1 (34.2–37.0)

C: 36.8 (34.3–37.5)

p=0.09

I_{≤10 min}: 36.2 (33.9–37.0)

C: 36.2 (34.3–37.1)

P= 0.19

Groups comparable at baseline?

Maternal characteristics were similar between the two interval groups. Monochorionicity was associated with a shorter delivery interval (p=0.01; 0.02).

Inter-twin interval ≤ 30 minutes

Inter-twin interval ≤ 10 minutes

Inter-twin interval > 30 minutes

Inter-twin interval > 10 minutes

Length of follow-up:

Not reported

Loss-to-follow-up:

Not reported

Incomplete outcome data:

Not reported

Outcomes reported for the 2^nd twin.

Mode of delivery twin 2, n (%)

Spontaneous vertex

I_{≤30 min}: 95/317 (30.0%)

C: 9/28 (32.1%)

p=0.83

I_{≤10 min}: 42/164 (25.6%)

C: 62/181 (34.3%)

P=0.09

Instrumental (forceps

or vacuum)

I_{≤30 min}: 55/317 (17.4%)

C: 11/28 (39.3%)

p<0.01

I_{≤10 min}: 10/164 (6.1%)

C: 56/181 (30.9%)

p<0.01

Breech

I_{≤30 min}: 163/317 (51.4%)

C: 5/28 (17.9%)

p<0.01

I_{≤10 min}: 112/164 (68.3%)

C: 56/181 (30.9%)

p<0.01

Caesarean section

I_{≤30 min}: 4 /317(1.2%)

C: 3/28 (10.7%)

p=0.01

I_{≤10 min}: 0/164 (0%)

C: 7/181 (3.9%)

0.01

Emergency caesarean section, n (%)

I_{≤30 min}: 4/317 (1.3%)

C: 3/28 (10.7%)

p=0.01

I_{≤10 min}: 0/164 (0.0%)

C: 7/181 (3.9%)

p=0.01

Admission to NICU, n (%)

I_{≤30 min}: 75/317 (23.7%)

C: 6/28 (21.4%)

p=0.79

I_{≤10 min}: 39/164 (23.8%)

C: 42/181 (23.2%)

P=0.90

Length of stay in NICU, days,

median (IQR)

I_{≤30 min}: 6.0 (4.0–15.0)

C: 6.5 (4.0–10.5)

p=0.21

I_{≤10 min}: 7.5 (4.0–17.7)

C: 6.0 (4.0–12.0)

P=0.56

Apgar score at 5 min <7, n (%)

I_{≤30 min}: 21/317 (6.6%)

C: 5/28 (17.9%)

p=0.03

I_{≤10 min}: 11/164 (6.7%)

C: 15/181 (8.3%)

P=0.58

Cord lactate >4.0 mmol/L, n (%)

I_{≤30 min}: 140 (62.2%)

C: 12 (80.0%)

p=0.17

I_{≤10 min}: 70 (57.9%)

C: 82 (68.9%)

P=0.08

Jaundice, n (%)

I_{≤30 min}: 171/317 (53.9%)

C: 18/28 (64.3%)

P=0.29

I_{≤10 min}: 92/164 (56.1%)

C: 97/181 (53.6%)

P=0.64

Sepsis, n (%)

I_{≤30 min}: 35/317 (11.0%)

C: 1/28 (3.6%)

P=0.33

I_{≤10 min}: 18/164 (11.0%)

C: 18/181 (9.9%)

P=0.75

Leung, 2002

Type of study:

A retrospective study

Setting and country: a university teaching hospital over a period of four years and nine

months, China (Hong Kong)

Funding and conflicts of interest:

No funding or conflicts of interest are reported in the article.

Inclusion criteria:

-twin deliveries

Exclusion criteria

-Delivery before 34 weeks of gestation.

-The first twin (Twin 1) delivered by caesarean section.

-Intrauterine death of either one of the twins before the

onset of labour.

-Discordant growth as defined by the discrepancy of

birthweight by more than 20%.

-Pregnancies complicated by pre-eclampsia, intrauterine

growth restriction, twin–twin transfusion or fetal

malformations.

N total at baseline:

N=118 twin pregnancies

-0-15 min: n=52

-16-30 min: n=51

->30 min: n=15

Important prognostic factors²:no table with baseline characteristics was given.

The mean maternal age was 29.7 years. Forty-eight (40.7%) of them were nulliparous. Twenty-six (22%) of

all twin pregnancies resulted from assisted reproductive

procedures. The mean gestation at delivery was 37.1 weeks. Thirty seven (31.4%) were delivered between 34 and 37 weeks. In 76 women Twin 1 (64.4%) had a normal vaginal delivery while the rest had an assisted vaginal delivery.

Groups comparable at baseline?

Not reported.

Twin-to-twin delivery interval (defined as the time

interval between the deliveries of the first twin and that of the second twin): 0-15 minutes

All uncomplicated twin

pregnancies with the first twin in cephalic presentation were

allowed a trial of labour, regardless of the presentation of the

second twin.

Twin-to-twin delivery interval (defined as the time

interval between the deliveries of the first twin and that of the second twin): 16-30 minutes; >30 minutes

Length of follow-up:

Not reported

Loss-to-follow-up:

Not reported

Incomplete outcome data:

Not reported

Mode of delivery of 2^nd twin

Normal delivery

0-15 min: 28

16-30 min: 17

>30 min: 1

Vaginal breech

0-15 min: 16

16-30 min: 15

>30 min: 2

Instrumental

0-15 min: 6

16-30 min: 11

>30 min: 2

Caesarean

0-15 min: 2

16-30 min: 8

>30 min: 10

Umbilical arterial pH 2^nd twin

The arterial pH was less than 7.0 in seven of the second

twins (6.6%).

The umbilical arterial pH of Twin 2 was less than 7.00 in none of the cases if delivered within 15 minutes after birth of Twin 1; 5.9% if within 16–30 minutes, and 27% if more than 30 minutes.

Lindroos, 2018

Type of study: retrospective study

Setting and country: university teaching hospital between January 2008 and December 2014, Sweden

Funding and conflicts of interest:

Financial support was received from the Health & Medical Care Committee

of the Regional Executive Board, Region Västra Götaland (VGFOUREG) and through an agreement concerning research and the education of doctors (ALFGBG-70940). Funding bodies had no role in the design of the study and

collection, analysis, interpretation of data and in writing the manuscript.

The authors declare that they have no competing interests

Inclusion criteria:

-twin delivery

Exclusion criteria:

-delivery before 32 weeks of gestation

-the first twin delivered by cesarean section (CS)

-intrauterine death of one or both twins before onset of labor

-known fetal malformations or chromosome

aberrations in one or both twins

-monoamniotic twin gestations

N total at baseline:

N=527 twin pregnancies

Intervention: ≤ 30 min, n=360

Control: >30 min, n=167

Important prognostic factors²:

Baseline characteristics for the n=527 twin deliveries.

Maternal age ± SD:

32.5±4.8

Nulliparous, n(%)

202 (38.3%)

Dichoriotic/diamniotic twin gestations

386/501 (77.0)

Monochoriotic/diamniotic twin gestations

115/501 (23.0)

Groups comparable at baseline?

Unknown. Baseline characteristics are not depicted for the intervention group (time interval ≤30 min) and control group (time interval >30 min) separately.

twin-to-twin time interval ≤30 minutes

All twin pregnancies

with the first twin in cephalic presentation were planned for vaginal delivery. If the second twin was in transverse lie an attempt of external version, to either cephalic or breech presentation, was performed -if needed with intravenous terbutaline or nitroglycerin for uterus relaxation. If lack of effective spontaneous contractions, oxytocin was started and spontaneous vaginal delivery, in head or breech presentation, was preferred. If this failed an internal version and breech extraction were to be considered. Otherwise CS was performed. There

was no upper time limit for twin-to-twin time interval and if no complications occurred expectant management was

applied.

twin-to-twin time interval > 30 minutes

Length of follow-up:

Not reported

Loss-to-follow-up:

Not reported

Incomplete outcome data:

Chorionicity was unknown in 26 deliveries.

Outcomes reported for the 2^nd twin.

Apgar <7 at 5 min, n(%)

I: 8/360 (2.2%)

C: 1/167 (0.6%)

P=0.28

Acidosis in umbilical arterial blood gas with pH < 7.10

I: 18/290

C: 22/136

P=0.002

Admitted to NICU

I: 88/360

C: 35/167

P=0.44

Admittance to NICU >7 days

I: 54/88

C: 22/35

P=1.0

NICU, mean (SD),

median, (range) days

I: 11 (7.2) 10 (1–35)

C: 12 (7.7) 9 (2–37)

P=0.26

Septicemia (confirmed by positive blood culture

within 28 days after birth)

I: 2/360

C: 0/167

P=1.0

Necrotizing Enterocolitis (within 28 days after

birth)

I: 1/360

C: 0/167

P=1.0

Perinatal mortality (death after onset of labor and within 7 days after birth)

I: 2/360 (0.6)

C: 0/167

P=1.0

Neonatal mortality (death within 28 days after birth)

I: 0/360

C: 0/167

P=1.0

Mode of delivery of the second twin, n (%)

Spontaneous cephalic

288/527 (54.6%)

Spontaneous breech

123/527 (23.3%)

Breech extraction

 9/527 (1.7%)

Vacuum extraction

72/527 (13.7%)

Cesarean section

35/527 (6.6%)

Stein, 2008

Type of study: population-based cohort study

Setting and country: maternity hospitals in Hesse between January 1990 and December 2004, Germany

Funding and conflicts of interest: No funding or conflicts of interest are reported in the article.

Inclusion criteria:

-twin deliveries

Exclusion criteria:

-delivery before 34+0 weeks of gestation

-the first twin delivered by caesarean section

-intrauterine death of either one of the twins

before the onset of labour

-pregnancies complicated by twin-twin transfusion or fetal malformations

N total at baseline:

N=4110 twin pregnancies

2^nd twins

-1-15 min, n=3115 (75.8%)

-16-30, n= 674 (16.4%)

-31-45, n=178 (4.3%)

-46-60, n=71 (1.7%)

->60 min, n=72 (1.8%)

Important prognostic factors²:

Maternal age (>35 years), n (%)

-1-15 min: 329 (11%)

-16-30 min: 87 (13.9%)

-31-45 min: 24 (14.5%)

-46-60 min: 13 (18.8%)

->60 min: 12 (18.2%)

Sum: 465 (12.1%)

Gestational age (≤35 weeks) n (%)

-1-15 min: 636 (21%)

-16-30 min: 135 (20.1%)

-31-45 min: 30 (16.9%)

-46-60 min: 19 (26.8%)

->60 min: 11 (15.5%)

Sum: 831 (20.2%)

Groups comparable at baseline?

Maternal parameters, such as maternal age, obesity, previous caesarean section and previous vaginal deliveries, were not related to the increased time interval of the second twin. Gestational age was not associated with the time interval.

Inter-twin birth interval:

16-30 min; 31-45 min; 46-60; >60 min

In order to examine trends over time, the birth intervals were stratified into periods of 15 minutes.

Inter-twin birth interval:

1-15 minutes

Length of follow-up:

Not reported

Loss-to-follow-up:

Not reported

Incomplete outcome data:

Not reported

Mode of delivery, n(%)

Spontaneous delivery

-1-15 min*: 2623 (84.7%)

-16-30 min: 487 (72.3%),

OR=0.47 (95% CI 0.39-0.57)

-31-45 min: 115 (65%),

OR=0.33 (95% CI 0.24-0.46)

-46-60 min: 41 (58.6%),

OR=0.25 (95% CI 0.16-0.41)

->60 min: 47 (65%),

OR=0.34 (95% CI 0.21-0.56)

-Sum: 3313 (81%)

Vaginal assisted delivery

-1-15 min*: 228 (7.4%)

-16-30 min: 77 (11.4%),

OR=1.62 (95% CI 1.23-2.13)

-31-45 min: 22 (12.4%),

OR=1.79 (95% CI 1.12-2.85)

-46-60 min: 8 (11.4%),

OR=1.62 (95% CI 0.77-3.43)

->60 min: 5 (6.9),

OR=0.94 (95% CI 0.37-2.35)

-Sum: 340 (8.3%)

Caesarean section

-1-15 min*: 22 (0.7%)

-16-30 min: 79 (11.7%),

OR=18.9 (95% CI 11.7-30.5)

-31-45 min: 33 (18.6%),

32 (95% CI 18.2-56.3)

-46-60 min: 19 (27.1%),

OR=52.1 (95% CI 26.6-102)

->60 min: 19 (26%),

 OR=50.1 (95% CI 25.6-98)

-Sum: 172 (4.2%)

Manual extraction

-1-15 min*: 223 (7.2%)

-16-30 min: 31 (4.6%),

OR=0.62 (95% CI 0.42-0.91)

-31-45 min: 7 (4%),

OR=0.53 (95% CI 0.25-1.14)

-46-60 min: 2 (2.9%),

OR=0.38 (95% CI 0.09-1.56)

->60 min: 1 (1.4%),

OR=0.18 (95% CI 0.03-1.31)

-Sum: 264 (6.5)

Apgar 5 min <7, n (%)

-1-15 min*: 57 (1.9%)

-16-30 min: 27 (4.1%),

OR=2.26 (95% CI 1.42-3.59)

-31-45 min: 11 (6.3%),

OR=3.54 (95% CI 1.82-6.87)

-46-60 min: 5 (7%),

OR=4.02 (95% CI 1.56-10.35)

->60 min: 2 (2.9%),

 OR=1.58 (95% CI 0.38-6.62)

-Sum: 102 (2.5%)

Acidosis

(defined as umbilical artery pH<7.1)

-1-15 min*: 90 (3.1%)

-16-30 min: 68 (11%),

OR=3.82 (95% CI 0.76-5.31)

-31-45 min: 26 (15.9%),

OR=5.83 (95% CI 3.65-9.31)

-46-60 min: 9 (13.4%),

OR=4.8 (95% CI 2.31-9.99)

->60 min: 11 (16.9%),

OR=6.3 (95% CI 3.19-12.46)

-Sum: 204 (5.4%)

Admission NICU

-1-15 min*: 868 (27.9%)

-16-30 min: 213 (31.6%),

OR=1.2 (95% CI 1-1.43)

-31-45 min: 61 (34.3%),

OR=1.35 (95% CI 0.98-1.86)

-46-60 min: 27 (33.8%),

OR=1.59 (95% CI 0.98-2.58)

->60 min: 21 (29.2%),

OR=1.07 (95% CI 0.64-1.78)

-Sum: 1190 (29%)

Perinatal death

(defined as intrapartum death of the fetus after onset of labour or birth of a live baby,

dying within the first 7 days)

-1-15 min*: 6 (0.19%)

-16-30 min: 3 (0.45%),

OR=2.31 (95% CI 0.58-9.29)

-31-45 min: 0 (0%), OR= -

-46-60 min: 1 (1.4%),

OR=7.4 (95% CI 0.89-62.3)

->60 min: 1 (1.39%),

OR=7.3 (95% CI 0.87-61.42)

-Sum: 11 (0.3%)

*Reference category for OR was 1-15 min time interval.

Fetal lie (second twin)

Cephalic, n (%)

-1-15 min*: 2322 (74.6%)

-16-30 min: 431 (64%),

OR= 0.61 (95% CI 0.51-0.72)

-31-45 min: 108 (60.7%),

OR=0.52 (95% CI 0.38-0.72)

-46-60 min: 38 (53.5%),

OR=0.39 (95% CI 0.24-0.63)

->60 min: 42 (58.3%),

OR=0.48 (95% CI 0.3-0.77)

-Sum cephalic: 2941 (71.6%)

Breech, n (%)

-1-15 min*: 725 (23.3%)

-16-30 min: 194 (28.8%),

OR=1.34 (95% CI 1.11-1.61)

-31-45 min: 53 (29.8%),

OR=1.4 (95% CI 1.01-1.95)

-46-60 min: 17 (23.9%),

OR=1.04 (95% CI 0.6-1.81)

->60 min: 25 (34.7%),

OR=1.76 (95% CI 1.07-2.88)

-Sum breech: 1014 (24.7%)

Transverse, n (%)

-1-15 min: 64 (2.1%)

-16-30 min: 48 (7.1%),

OR=3.66 (95% CI 2.49-5.37)

-31-45 min: 17 (9.6%),

OR=5.03 (95% CI 2.88-8.78)

-46-60 min: 16 (22.5%),

OR=13.85 (95% CI 7.53-25.47)

->60 min: 5 (6.9%),

OR=3.55 (1.39-9.11)

-Sum transverse: 150 (3.7%)

*Reference category for OR was 1-15 min time interval.

Tal, 2018

Type of study: retrospective study

Setting and country: a single university teaching hospital between January 1995 and December 2015, Israel

Funding and conflicts of interest:

No funding or conflicts of interest are reported in the article.

Inclusion criteria:

-pregnant women with twin gestation who had a trial of labor and delivered the first twin vaginally (regardless of mode of delivery of the second twin)

-a gestational age of 24 weeks or more

Exclusion criteria

-monoamniotic

twins

-twins with major malformations or complicated

with antepartum fetal death of one or both twins

-women who had a planned cesarean delivery or any

indicated cesarean delivery without a trial of labor

N total at baseline:

Intervention: <30 min, n=596

Control: ≥30 min, n=117

Important prognostic factors²:

Maternal age ± SD:

I: 29.8 ± 5.1

C: 30.4 ± 5.2

Dichorionic, n (%)

I: 461 (77.4%)

C: 101 (86.3%)

Monochorionic diamniotic, n (%)

I: 98 (16.4%)

C: 9 (7.7%)

Unknown chorionicity, n (%)

I: 37 (6.2%)

C: 7 (6.0%)

Primiparous, n (%)

I:189 (31.7%)

C: 43 (36.8%)

Use of any fertility treatments in index pregnancy, n (%)

I: 131 (22.0%)

C: 55 (47.0%)

Gestational age at delivery, weeks

I: 36.2 ± 2.9

C: 36.1 ± 3.2

Groups comparable at baseline?

Women who used fertility treatments to become pregnant (p=.001) or had dichorionic twins (p=.02) were at greater risk to have an interval of 30 minutes or more.

Inter-twin delivery interval < 30 minutes

After delivery of the first twin, expectant management was employed during the study period regardless of second

twin presentation.

The preferred method for delivering the breech second twin is assisted

breech delivery.

Inter-twin delivery interval ≥ 30 minutes

Length of follow-up:

Not reported

Loss-to-follow-up:

Not reported

Incomplete outcome data:

Only reported for the outcome measure Presentation of second twin after delivery of the first twin.

Intervention:

6 (1.0%)

Reasons not described.

Control:

C: 1 (0.9%)

Reasons not described.

Mode of delivery of second twin, n (%)

Spontaneous vaginal

I: 552/596 (92.6%)

C: 88/117 (75.2%)

Reference

Vacuum

I: 25/596 (4.25%)

C: 7/117 (6.0%)

RR=1.70 (95% CI 0.76-3.82)

Cesarean

I: 19/596 (3.2%)

C: 22/117 (18.8%)

RR=6.01 (95% CI 3.37-10.72)

Second twin cord artery pH < 7.1, n (%)

I: 17/596 (2.8%)

C: 5/117 (4.3%)

RR=1.50 (95% CI 0.56-3.98)

Second twin Apgar score at 5 minutes <7, n (%)

I: 12/596 (2.0%)

C: 0/117 (0.0%)

RR=0.23a (95% CI 0.01-3.68)

a Adjusted; 0.5 added to each cell

Any postpartum haemorrhage, n (%)

I: 41/596 (6.9%)

C: 5/117 (4.3%)

RR=0.62 (95% CI 0.25-1.54)

Intrapartum death of one neonate, n (%)

I: 0 (0.0%)

C: 0 (0.0%)

RR (95% CI): -

Neonatal death of one neonate, n (%)

I: 3 (0.5%)

C: 0 (0.0%)

RR= 0.76a (95% CI 0.05-12.38)

aAdjusted; 0.5 added to each cell

Neonatal death of both neonates, n (%)

I: 2 (0.3%)

C: 1 (0.8%)

RR=2.55 (95% CI 0.23-27.86)

Presentation of second twin after delivery of the first twin, n (%)

Vertex

I: 432 (72.5%)

C:77 (65.8%)

Reference

Breech

I: 149 (25.0%)

C: 33 (28.2%)

RR=1.17 (95%CI 0.85-1.61)

Transverse

I: 9 (1.5%)

C: 6 (5.1%)

RR=3.54 (95% CI 1.30-9.69)

Missing data

I: 6 (1.0%)

C: 1 (0.9%)

RR=0.94 (95% CI 0.11-7.67)

Study reference

(first author, year of publication)

Bias due to a non-representative or ill-defined sample of patients?¹

(unlikely/likely/unclear)

Bias due to insufficiently long, or incomplete follow-up, or differences in follow-up between treatment groups?²

(unlikely/likely/unclear)

Bias due to ill-defined or inadequately measured outcome?³

(unlikely/likely/unclear)

Bias due to inadequate adjustment for all important prognostic factors?⁴

(unlikely/likely/unclear)

Algeri 2019

Unlikely

Unlikely

Outcomes of interest available for all included second twins.

Unlikely

Unlikely

Monochorionicity was more frequent in case of shorter intertwin delivery interval (30.1 versus 14.3%, p=.05). Multivariate regression analysis was performed.

Cukierman 2019

Unlikely

Unlikely

Outcomes of interest available for all included second twins.

Unlikely

The outcome measure sepsis was not further defined.

Unlikely

Maternal characteristics were similar between the two interval groups. Monochorionicity was associated with a shorter delivery interval (p=0.01; 0.02). Multivariate regression analysis was performed.

Leung 2002

Unlikely

Unlikely

Outcomes of interest available for all included second twins.

Unlikely

Unlikely

Only uncorrected, descriptive data were given.

Not reported if groups were comparable at baseline.

Lindroos 2018

Unlikely

Unclear

There were missing umbilical arterial blood gas pH values in 101/527 (19.2%) second twins. Reasons not given.

Unlikely

Unclear

Baseline characteristics are not depicted for the intervention group (time interval ≤30 min) and control group (time interval >30 min) separately (i.e, only showed for total group).

Only uncorrected, descriptive data were given.

Stein 2008

Unlikely

Unlikely

Outcomes of interest available for all included second twins.

Unlikely

Unlikely

Only uncorrected, descriptive data were given.

Maternal parameters and gestational age were not associated with the time interval.

Tal 2018

Unlikely

Unlikely

Outcomes of interest available for all included second twins.

Unclear

The outcome measure ‘any postpartum haemorrhage’ was ill-defined. Neonatal death was not further defined.

Unlikely

Only uncorrected, descriptive data were given.

Women who used fertility treatments to become pregnant (p=.001) or had dichorionic twins (p=.02) were at greater risk to have an interval of 30 minutes or more.