Results
This study included 39 MC twins following sIUD. Among these cases, 89.7% (35/39) of cases were PTB and 10.3% (5/39) of cases were full term birth. The incidence of spontaneous PTB was 66%. Furthermore, 87.2% (34/39) of cases had spontaneous death and 12.8% (5/39) of cases had spontaneous death after fetoscopic laser occlusion. The maternal ages were 20-41 years with the mean maternal age being 30.6 years. The mean gestational age of sIUD was 27.4 (17-35) weeks. The mean gestational age of birth was 32.8 (27-40) weeks. 23.1% (9/39) of cases had maternal complications (4 cases of gestational hypertension, 5 cases of gestational diabetes mellitus). 38.4% (15/39) of cases had fetal complications (10 cases of twin-twin transfusion syndrome, 5 cases of selective intrauterine growth restriction). 46.34% (19/39) of patients conceived naturally. 5.12% (2/39) of patients underwent assisted reproductive conception. 23.1% (9/39) of cases had premature rupture of fetal membranes. 17.9% (7/39) of cases had abnormality in amniotic fluid (4 cases of hydramnios, 3 cases of hypamnion). 29 cases were spontaneous labor (including 26 preterm birth cases and 3 full term birth cases) and 10 cases underwent cesareean section due to obstetrical factors.
We compared the differences between the preterm birth group and the full term birth group (Table 1). We found that the gestational age of sIUD was a risk factor for preterm birth (p<0.05). We conducted multi-factor analysis for the above factors (Table 2). We also found that the gestational age of sIUD was a risk factor of preterm delivery (p<0.05) with OR>1, suggesting that higher gestational age of sIUD led to a higher risk of preterm birth.
To analyze the differences between the gestational age of sIUD and the gestational age of birth, we divided the cases into four groups according to the gestational age of sIUD (14-19 weeks, 20-24 weeks, 25-30 weeks, 31-36 weeks). We found that the 25-30 weeks at sIUD group had the youngest gestational age at birth (31.7 weeks) and 14-19 weeks at sIUD group had the oldest gestational age at birth (38.33 weeks) (Figure 1). Because the numbers representing the weeks in the third trimester are bigger than the numbers representing the weeks in first and second trimesters, we noticed that the numerical gestational age at birth will increase accordingly. Therefore, we used the timing of the surviving twin’s prolonged gestational age after sIUD, rather than the surviving twin’s absolute gestational age at birth, to analyze the trend in the four groups (Figure 2). We found that increases in the gestational age at sIUD was associated with shorter prolongation of gestational age in the surviving twin.
In the above cases, we found that some cases had iatrogenic PTB due to obstetric factors. Therefore, we wanted to exclude human intervention and re-analyze the relationship between the gestational age of sIUD and the gestational age of birth in cases of spontaneous PTB. In this study, there were 26 spontaneous PTB cases. After re-analysis, we found that the gestational age of sIUD was still the main risk factor of preterm birth (p<0.05). In addition, we found that OR<1 in this association, meaning that older gestational age at sIUD was associated with younger gestational age at delivery (table 3). In order to further analyze the relationship between sIUD and spontaneous PTB,we divided spontaneous PTB cases into four groups according to the gestational age at sIUD (14-19 weeks, 20-24 weeks, 25-30 weeks, 31-36 weeks). We found 25-30 weeks at sIUD group had the youngest gestational age at birth for the surviving twin (31.29 weeks) and 14-19 weeks at sIUD group had the oldest gestational age at birth for the surviving twin (36 weeks) (Figure 3). Because the numbers representing the weeks in the third trimester are bigger than the numbers representing the weeks in first and second trimesters, we noticed that the numerical gestational week at birth will increase accordingly. Therefore, we calculated the amount of gestational weeks prolonged after sIUD to reach delivery, rather than the absolute gestational age at birth, to analyze the trend in the four groups (Figure 4). We found that in spontaneous PTB cases, increases in the gestational age at sIUD was associated with shorter prolongation of gestational age in the surviving twin. This trend was consistent in all MC twins cases and spontaneous PTB cases.