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.