Maternal and neonatal outcomes for the different transfer
strategies
Maternal and neonatal outcomes for all FET cycles and in each group are
summarized in Table 1. Maternal and neonatal outcomes for the four
groups were statistically different for biochemical pregnancy, clinical
pregnancy, monozygotic twins, miscarriages, maternal complications, live
births, twin births, preterm births, low birth weight and SGA
(P<0.05). Results of pairwise comparisons for maternal and
neonatal outcomes between the groups are shown in Table S1. Percentages
for each maternal or neonatal outcomes for each group are shown in
Figure 2.
Among the four groups, the
biochemical pregnancy rate, the
clinical pregnancy rate, and the live birth rate were the lowest in the
C-1 group (24.1%, 21.5% and 11.8%, respectively) and were the highest
in the B-2 group (59.1%, 53.0% and 33.6%, respectively). However,
this was accompanied with higher risks of miscarriages (21.2%),
maternal complications (11.9%), twin births (28.9%), preterm births
(21.2%) and low birth weight (17.7%) (P<0.008,
Bonferroni-corrected p-value for multiple pairwise comparisons). The
biochemical pregnancy rates, the clinical pregnancy rates and the live
birth rates in the C-2 group and B-1 group were statistically different
(46.7% vs 50.0%, 42.1% vs 44.3%, 29.0% vs 23.0%, respectively),
with different risks for monozygotic twins, miscarriages, twin births,
preterm births, low birth weights and SGA (P<0.008). These
results demonstrated that the double cleavage-stage embryo transfer
strategy and the single blastocyst-stage embryo transfer strategy were
preferential among the four groups. Hence additional comparisons between
the C-2 and B-1 groups were performed.
In this study, 20 cases (0.3%) of congenital malformations were
reported among live births and included one case (1.1%) in the C-1
group, 12 cases (0.3%) in the C-2 group, 6 cases (0.3%) in the B-1
group, and one case (0.1%) in the B-2 group. However, due to the
limited sample size, comparisons of congenital malformations between the
groups were not performed.
In addition, comparisons were performed between the double-cleavage
transfer (C-2) and the single-blastocyst transfer (B-1) group. After
adjusting for maternal age, BMI, infertility type, cause of infertility,
duration of infertility, type of fertilization in the current cycle and
previous ART cycles, the biochemical pregnancy rates and
the clinical pregnancy rates between
two groups were not statistically different (aOR for the biochemical
pregnancy rate, 1.07; 95% CI, 1.00-1.15; and aOR for the clinical
pregnancy rate, 1.04; 95% CI, 0.97-1.12); and the live birth rate in
the B-1 group was lower compared to the C-2 group (aOR, 0.78; 95% CI,
0.72-0.85). With regards to negative outcomes, compared to the C-2
group, the B-1 group had a higher risk for monozygotic twins (aOR, 3.02;
95% CI, 1.79-5.10) and miscarriages (aOR, 1.29; 95% CI, 1.11-1.51) but
had a lower risk for twin births (aOR, 0.06; 95% CI, 0.04-0.09),
preterm births (aOR, 0.51; 95% CI, 0.41-0.65), low birth weights (aOR,
0.30; 95% CI, 0.22-0.40) and SGA (aOR, 0.51; 95% CI, 0.33-0.77)(.
Maternal age is often considered as one of the most important
determinants for maternal and neonatal outcomes for any type of ART
cycle. Therefore, maternal or neonatal outcomes between the C-2 group
and B-1 group and probabilities for each maternal age group (20-29 years
old, 30-34 years old, 35-37 years old, 38-39 years old, 40-42 years old
and >42 years old) were calculated. Results are shown in
Figure 3 (Detailed results are shown in Table S2 and Table S3).
With regards to the C-2 group, the probability of biochemical pregnancy
and clinical pregnancy declined from 0.55 and 0.50 at 20-29 years old to
0.27 and 0.22 at >40 years old. Of the cycles with clinical
pregnancy, the probability of monozygotic twins decreased from 0.008 to
0.005, the probability of miscarriages increased from 0.11 to 0.31 and
the probability of maternal complications increased from 0.09 to 0.20 at
the same maternal age intervals. The probability of live birth declined
from 0.30 at 20-29 years old to 0.11 at >40 years old.
Among those cycles with live births, the probability of twin births
declined from 0.28 to 0.11, and the probabilities of preterm births, low
birth weights, and SGA slightly fluctuated from 0.14 to 0.18, 0.12 to
0.15 and 0.05 to 0.06, respectively. (Detailed results are shown in
Table S4).
With regards to the B-1 group, the probability of biochemical pregnancy
and clinical pregnancy declined from 0.56 and 0.51 at 20-29 years old to
0.28 and 0.22 at >40 years old. Among those cycles with
clinical pregnancy, the probability of monozygotic twins decreased from
0.023 to 0.011, the probability of miscarriages increased from 0.13 to
0.34 and the probability of maternal complications increased from 0.08
to 0.16 at the same maternal age intervals. The probability of live
birth declined from 0.25 at 20-29 years old to 0.08 at >40
years old. Among the cycles with live births, the probability of twin
births, preterm births, low birth weight, and SGA slightly fluctuated
from 0.01 to 0.02, 0.07 to 0.10, 0.04 to 0.05 and 0.02 to 0.03,
respectively.