Birth outcomes
Prematurity
All included trials involving 4845 participants reported the prematurity, with 2363 pregnant women were randomized assigned to receive DP, 2482 were randomized assigned to receive SP 13, 14, 22-24. The occurrence of prematurity did not differ significantly between the DP and SP groups (RR=1.02; 95%CI, 0.87–1.19; P = 0.83; I²=0.00%; Figure S1; see Supplementary Material). Figure 4-A showed that the occurrence of prematurity did not differ significantly between the IPT-DP-4-6w and IPT-SP-4-6w, IPT-DP-8w and IPT-SP-8w groups(RR=1.00; 95%CI, 0.70–1.41; P = 0.98; I²=10.20%; Figure 4-A). Figure 4-B showed no significant differences were obtained for prematurity between IST-DP with IPT-SP-4-6w (RR=1.06; 95%CI, 0.89–1.27; P = 0.51; I²=4.50%; Figure 4-B).
Low birth weight
Figure B showed that five articles, with a total of 4644 participants, reported the incidence of low birth weight13, 14, 22-24. 2267 randomly assigned to DP group, 2377 randomly assigned to SP group. DP has similar effect compared with SP(RR=1.06; 95%CI, 0.88–1.29; P = 0.524; I²=19.2%; Figure S2). The subgroup analysis indicated similar rates of low birth weight were noted between different intervals of SP and DP(RR=1.00; 95%CI, 0.73–1.38; P = 0.99; I²=0.00%; Figure 5-A). We noted that IST-DP, compared with IPT-SP-4-6w, presented similar rates (RR=1.24; 95%CI, 0.96–1.61; P = 0.10; I²=0.00%; Figure 5-B).
Overall mortality (stillbirth and spontaneous abortion)
Four trials reported the effect of DP and SP on stillbirth (RR=0.66; 95%CI, 0.42–1.05; P = 0.09; I²=33.20%;Figure S3; see Supplementary Material) and three trials reported the incidence of small for gestational age (RR=0.38; 95%CI, 0.03–5.35; P = 0.34; I²=75.60%; FigureS4; see Supplementary Material). The subgroup analysis showed different intervals and regimens of DP were not associated with a better effect of SP (Figure 6-A, Figure 6-B and Figure 7).
Small for gestational age
The incidence of small for gestational age was evaluated in three trials, including 4242 participants, and non-significant reduction was found between DP and SP groups(RR=1.12; 95%CI, 0.91–1.37; P = 0.293; I²=0%; Figure S5; see Supplementary Material). Figure 8 showed IPT-DP-4-6w has similar effects to IPT-SP-4-6w(RR=0.99; 95%CI, 0.72–1.37; P = 0.63; I²=0.00%; Figure 8-A)and IST-DP had similar effects to IPT-SP-4-6w (RR=1.22; 95%CI, 0.96–1.56; P = 0.11; I²=0.00%; Figure 8-B)