We found statistically significantly higher LBR among the fresh-cycle patients. Whilst our frozen cycle group is considerably smaller than the other group, our result agrees with Stormlund et al’s study.6 They found that among regularly menstruating women, frozen strategy did not improve the LBR when compared to fresh cycle strategy.6 Their findings warrant caution towards the use of liberal frozen cycle strategy in the absence of strong indications such as ovarian hyperstimulation syndrome (OHSS) and preimplantation genetic testing (PGT).6
Our study found that among patients with ovulatory disorder, there was a significantly different proportion in LBR between the fresh cycle group (10/47, 17.5%) and the frozen group (7/16, 43.8%) (p= 0.04). However, there was no significant difference in the biochemical pregnancy rate of the 2 groups (p=0.2). This is similar to Chen et al’s study.7 They found that among patients with polycystic ovarian syndrome (PCOS), FET resulted in significantly higher number of live births despite no significant difference in biochemical pregnancy rate.7 This is a promising finding, as this would suggest that for those with PCOS, FET should be advocated to produce higher LBR. Furthermore, the relationship shown by Chen et al was replicated in our study, despite our smaller number of subjects.
We found that among patients with endometriosis, there was no significantly different proportion in the biochemical pregnancy and LBR between the groups (p>0.999; p=0.361 respectively). Results have been conflicting. Mohamed et al & Bourdon et al reported that deferred embryo transfer through frozen strategy was significantly associated with higher cumulative pregnancy rate.3,8 However, Feichtinger et al reported the opposite.9 Again, the lack of difference in our study might have been due to the lack of power as the number of endometriosis patients in our dataset was <50.
We discovered that there were roughly similar live birth rates among mothers ≤30 years old and >30 years old in the fresh cycle group. However, in the frozen cycle group, mothers aged >30 years old significantly delivered more neonates than those ≤30 years old. This is different from a very large-scale study in China by Zhu et al.10 Another study by Wang et al, though, could possibly corroborate our results.11 They found that among women whose progesterone concentration >1 ng/mL, increasing age was associated with significantly higher LBR with freeze-only transfer cycles.11 Whilst progesterone was not measured among our patients, the rising progesterone might have been the reason behind the very high success rates for frozen cycles among those >30 years old.11
The lack of association between presence of excellent embryos and live birth rates in FET was surprising, despite the presence of such association among ET cycles. Whilst our lack of association is surprising, it might have been due to the relatively few pregnancies from FET patients over 1.5 years of data recruitment in our study. Another reason might have been due to suboptimal endometrium among our patients. With more patients opting for the frozen cycle at our facility, more data would be generated to allow for a repeat and more powerful analysis in the future.
The frozen cycle was associated with higher median birthweight (3200 (3009-3654) than the fresh cycle neonates (2800 (2200-3900)). Despite this association not being statistically significant, the trend was present and we suspect that the lack of significance was due to the fewer subjects of the frozen group when compared to the fresh cycle group. This was seen in the overall birthweight comparison, as the median birthweight of the freeze-cycle neonates (whilst not adjusting for the order of pregnancies) was statistically significantly higher than the fresh cycle neonates (p=0.01). This may have been due to the good quality of the cryopreserved embryos.12 Furthermore, the lower birthweight among fresh ETs might have been caused by the higher likelihood of abnormal placentation due to the over-estrogenized uterine environment.12
Our study’s strengths include the following. First, it is the first for our centre and to our knowledge, the first in our country to publish IVF data and compare the outcomes of fresh cycle IVFs against frozen-cycle IVFs. Second, our centre is among the top centres with high IVF cycles per year in Indonesia and our patients originate not just from the neighbouring cities but also from distant provinces.
To conclude, we did not find any significant differences in both the biochemical pregnancy rate and the LBR between frozen cycles and fresh cycles. We also failed to observe significant differences in the LBRs when stratified according to the aetiology of infertility except by their ages.