In-vitro fertilisation (IVF) has come a long way from being a single-step laboratory process to a deeply personalised treatment pathway. Yet, even with genetically healthy embryos and precise transfers, some cycles fail inexplicably. Scientific evidence has started pointing to a less obvious factor: the timing of implantation. This ‘window’ of receptivity in the endometrium, once thought to be universally predictable, is now recognised as unique to each woman says Dr Sonali Mandal Bandyopadhyay, Fertility Specialist at Birla Fertility & IVF, Howrah.
The hidden variable in failed cycles
Traditionally, embryo transfer is performed five days after progesterone initiation during a frozen embryo transfer cycle. However, trial studies suggest that in nearly 20–25% of women with recurrent implantation failure, the endometrial lining may not be receptive at the expected time. In such cases, even a perfect embryo cannot attach, simply because the uterus is out of sync with it. This subtle asynchrony, often invisible to ultrasound or hormone monitoring, has emerged as one of the most significant hidden causes of IVF failure.
Evidence behind endometrial receptivity testing
Recent research has validated the use of endometrial receptivity testing (ERT) to map the exact molecular signature of receptivity. Through the analysis of hundreds of gene expressions from a small biopsy sample, the test identifies when the uterine lining is truly “ready.” A meta-analysis in Reproductive Biology and Endocrinology reported improved implantation and pregnancy rates when embryo transfer was adjusted according to receptivity results, particularly among women with two or more failed IVF attempts.
The rise of personalised embryo transfer
Armed with these insights, a new strategy is employed, known as personalised embryo transfer (pET). Instead of following a fixed schedule, the embryo is transferred precisely when the patient’s unique window of implantation opens – whether earlier or later than the standard timeline. Studies indicate AZthat this approach can enhance implantation success in patients with recurrent failure, marking a shift from standardised to precision-based fertility care.
Towards a more individualised IVF future
The understanding that every uterus operates on its own timeframe has changed the narrative around IVF failures. Rather than attributing unsuccessful cycles solely to egg or embryo quality, modern fertility science recognises the endometrium as an active, dynamic participant. Personalised timing, guided by receptivity testing, represents a critical step in bridging the gap between embryo potential and implantation success, bringing science closer to the quiet precision that nature once perfected.