Motherhood
Frozen embryo transfers in IVF linked to greater risk of maternal hypertension
Implications rise with increasing use of embryo freezing in assisted reproduction
Concerns have been raised that pregnancies derived from frozen embryo transfers in IVF might increase the maternal risk of hypertensive disorders.
Pre-eclampsia is one such condition that causes high blood pressure during pregnancy and after labour and which may have severe consequences for both the mother and the foetus.
The concerns have been raised in recent observational studies comparing the outcomes of fresh and frozen transfers, which, by definition, are subject to statistically confounding variables. Sibling comparisons can remove much of this confounding.
The extensive study based on real-life registry data and a comparison of maternal complications in sibling pregnancies indicate that pregnancies following frozen embryo transfer (FET) do indeed have a substantially higher risk of hypertensive disorders than naturally conceived pregnancies.
This same raised risk was also found in a sub-group analysis of sibling births, which was designed to eliminate the effect of any parental factors in the results.
“Our findings are important because the number of FETs is rapidly increasing throughout the world,” says the study’s first author, Dr Sindre H. Petersen from the Norwegian University of Science and Technology.
He has presented the study results at the 38th annual meeting of ESHRE in Milan on behalf of the Committee of Nordic Assisted Reproductive Technology and Safety group which monitors the health of mothers and children born after assisted reproduction in the Nordic countries.
According to the latest registry report from ESHRE, the proportion of FET cycles relative to fresh is still on the rise in Europe. In 2017 the proportion was 49 per cent, against 38 per cent in 2014. Similar trends are present in the US and most high-income countries.
FETs are increasingly common because of improved cryopreservation methods, facilitation of single embryo transfer, reduction of ovarian hyperstimulation, and the elective freezing of all embryos.
The study analysed more than 4.5 million singleton pregnancies in the registries of three Nordic countries with delivery between 1988 and 2015. Of the conceptions following assisted reproduction, 78, 300 were after fresh embryo transfer and 18,037 were after FET.
The registry birth references – largely unique to the Nordic countries – also allowed the identification of 33,209 sibling deliveries following either fresh or frozen embryo transfer, and natural conception.
“This study was by far the largest sibling analysis to date investigating the association between assisted reproduction treatments and hypertensive disorders in pregnancy,” Dr Petersen adds.
Results of the study showed that the risk of hypertensive disorders in pregnancy were almost twice as high in the pregnancies following FET that in pregnancies following a natural conception. However, the risk of hypertensive disorders in pregnancies following fresh embryo transfer pregnancies was comparable to naturally conceived pregnancies.
Hypertensive disorders in pregnancy comprise gestational hypertension and pre-eclampsia, and the more rare but severe conditions of eclampsia and Hemolysis-Elevated-Liver-enzymes-Low-Platelets (HELLP) syndrome.
Adjustments for maternal body mass index, smoking and time between deliveries did not affect the end results, nor did other methods of assisted reproduction (IVF, ICSI, duration of embryo culture or number of embryos transferred).
Dr Petersen says that the design of the study was not able to assess the relative merits of embryo freezing against the higher risk of hypertensive disorders, but notes that “cryopreservation has facilitated the highly favourable single embryo transfer approach, improving foetal and maternal outcomes by avoiding multiple pregnancies”.
Recent studies have suggested that the risk of hypertensive disorders in FET pregnancies may be associated with therapies to prepare the uterus for embryo implantation. These are usually given in the form of hormone replacement therapy in what has become known as a ‘programmed’ or ‘artificial’ cycle – in which there is no naturally developing corpus luteum to provide hormonal support for the pregnancy.
The presence of a corpus luteum – a mass of cells that forms in an ovary responsible for the production of the hormone progesterone during early pregnancy – is one potentially important difference between natural conception and fresh embryo transfers, on the one hand and FETs, on the other, says Petersen.
He adds: “In our analysis all natural conceptions and fresh embryo transfer pregnancies had a corpus luteum, while a subset of the FET pregnancies did not.
“However, we expect from previous Danish and Swedish publications that in our study, only 15-30 per cent of FET pregnancies were in artificial cycles, which seems unlikely to drive the entirety of the strong association in our results.
“It thus seems possible that some inherent aspect of the freezing and thawing process, for example epigenetic changes, might be responsible as well.”
The doctor has pointed out that it is too early to recommend changes to treatment strategies based solely on this study, and that there are still good reasons why frozen embryo transfers are increasingly used, especially in their facilitation of single embryo transfer.
“I am confident that a well-grounded and individualised decision of whether to go for a fresh or a frozen cycle can be made after dialogue between the clinician and the couple,” he concludes.
“Our study can contribute to informed decision-making for patients and clinicians.”
Early birth may cut serious complications and stillbirth risk in high blood pressure pregnancies without increasing caesarean rates, a Cochrane review suggests.
Planned early birth after 34 weeks cut serious maternal complications by nearly half compared with watchful waiting, the findings suggest.
It also likely reduced the risk of stillbirth by about 75 per cent, although the authors said this should be interpreted with caution.
Catherine Cluver, senior author of the review and researcher at Stellenbosch University and Tygerberg Hospital, said: “These findings give clinicians and women clearer guidance about the timing of birth when high blood pressure develops in pregnancy.
“For women with pre-eclampsia in particular, the evidence supports offering planned early birth from 34 weeks, and no later than 37 weeks.”
This Cochrane review, led by King’s College London, pooled data from six randomised controlled trials involving 3,491 women.
The trials compared planned early birth after 34 weeks with watchful waiting in women with one or more hypertensive disorders of pregnancy.
Hypertensive disorders of pregnancy, including pre-eclampsia, gestational hypertension and chronic hypertension, are the second leading cause of maternal death globally.
For women with pre-eclampsia, early birth remains the only definitive treatment, as the condition is driven by the placenta and will only resolve once it is delivered.
The trials took place in the Netherlands, UK, US, India and Zambia.
The review found high-certainty evidence that serious maternal complications were nearly halved in women who had planned early birth compared with those managed with watchful waiting.
The finding on stillbirth was based on moderate-certainty evidence and was driven by a single trial in India and Zambia, where stillbirth rates are higher. No stillbirths were recorded in the high-income country trials.
The review also found that planned early birth likely does not increase neonatal unit admission, although this finding was also based on moderate-certainty evidence.
The authors said the maternal benefit held across both high- and low-income settings, suggesting early birth reduces complications even when women are already receiving appropriate monitoring and care.
Alice Beardmore-Gray, lead author of the review and obstetrician at King’s College London, said: “Judging when to offer birth is the question that we battle with clinically every day.”
The authors added that in two of the trials, more than half the women allocated to watchful waiting ended up needing emergency birth before 37 weeks.
They typically gave birth just three to five days later than women allocated to planned early birth and often experienced more complications.
Beardmore-Gray said: “A common misconception is that by waiting longer, mum and baby are gaining more time, but often what you are doing is just delaying an inevitable emergency birth, when both may be in a worse condition.”
The review found high-certainty evidence of no increased risk of caesarean section associated with planned early birth.
Beardmore-Gray said: “That is the first question anyone asks when you offer them an early induction: won’t it increase my risk of a C-section?
“Being able to clearly answer no is a really important piece of information to give women when counselling them about the timing of their birth.”
The authors said the timing of birth should take into account the woman’s preferences and the severity of her condition.
They said these findings are consistent with and reinforce current international guidelines, which recommend that all women with pre-eclampsia should be offered planned early birth no later than 37 weeks.
Women with gestational hypertension or chronic hypertension without severe features may choose to continue with careful monitoring, with planned early birth considered from 39 weeks onwards.
Further research is needed on longer-term outcomes for infants born late preterm and on the long-term cardiovascular health of mothers affected by hypertensive disorders of pregnancy.
By Women’s HealthX
In recognition of World Maternal Mental Health Day, Women’s HealthX is placing a spotlight on one of the most urgent and under addressed areas in women’s health: maternal mental health and maternity care innovation.
Worldwide, 1 in 5 new mothers experiences a perinatal mood and anxiety disorder, yet up to 7 in 10 hide or downplay their symptoms.
Even within established care frameworks, this creates challenges for timely detection and treatment, highlighting the need for additional tools, insights, and system-level support to prevent long-term consequences for both mother and child.
Women’s HealthX convenes 750+ senior leaders from across the women’s health ecosystem, including pharma & biotech, hospitals, digital health innovators, solution providers, payers, enterprises & policy makers to explore how telehealth, predictive analytics, and digital health platforms are transforming maternal and postnatal care – from AI-driven early risk identification to remote monitoring solutions that keep mothers cognitively and emotionally supported long after they leave the clinic.
Key sessions on Maternity & Maternal Care with key industry leaders:
Key sessions dedicated to maternity and maternal mental health will address critical system challenges and opportunities for innovation, including fragmentation in care delivery, health inequities, and persistent maternal mortality rates in high income countries.
Featured speakers include:
Christina Pardo, medical director, women’s health, Weill Cornell Medicine NewYork Presbyterian, on “Bridge Existing Healthcare Gaps Caused by Fragmentation Between OB/GYN And Birth Workers.”
Gayatri Setia, director of preventive Cardiology, NYCHHC, on “Improve Patient Access to Prevention in Equalities and Discrimination in Maternity and Maternal Care”
Catherine Monk, founding director, Center for the Transition to Parenthood, Columbia University Irving Medical Center, on “Leveraging Developmental Neuroscience to Provide Improved Maternal Care”
Danielle Johnson, chief medical officer, Lindner Center of HOPE, on “Understanding the Scope of Disparities in Perinatal Mental Health”
Kimberley Sampson, chair of OB GYN, Southwestern Vermont Medical Center, on “Why Maternal Mortality Persists in High-Income Countries”
Erica Smith, VP value and access, Chiesi, on “Empowering Mothers, Advancing Equity, and Improving Outcomes in Premature Care”
A Call to Action for the Femtech Ecosystem
As femtech continues to mature, maternal mental health represents a critical frontier where technology, data, and clinical insight must converge.
Women’s HealthX provides a platform for collaboration and knowledge sharing to accelerate the development and adoption of solutions that deliver measurable impact for mothers and families.
From predictive analytics to personalized, continuous care models, the event underscores a central theme: meaningful transformation in women’s health begins with better data, stronger evidence, and cross sector collaboration.
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Only 9 days left to register for your chance to win a therapeutic massage at Encore Boston
Women’s HealthX is where the transformation of women’s health begins at its true foundation: data, science, and evidence.
About Women’s HealthX
Women’s HealthX is where the transformation of women’s health begins at its true foundation: data, science, and evidence.
It’s the leading event dedicated to closing the sex difference data gap and accelerating breakthroughs through science driven, real world case studies.
Taking place on December 3 to 4, 2026 in Boston, USA, the exhibition will bring together more than 750 healthcare leaders, including clinicians, payers, employers, investors, and policymakers.
7 different stages across 2 days with 150+ expert speakers taking an holistic approach to women’s health.
From fertility, maternity, sexual health, cognitive health, menopause and chronic disease, we address care at every stage of a woman’s life.
Opinion
What Maternal Mental Health Month reveals about where postpartum support actually breaks down
By Morgan Rose, chief science officer at Ema, and Lauren Scocozza, vice president of product at Willow
May is Maternal Mental Health Month, and every year it surfaces a familiar set of statistics: 1 in 5 new mothers experiences postpartum depression or anxiety, most go unscreened, and the majority who are screened don’t receive adequate follow-up care.
The conversation is important. But the numbers obscure something that anyone who has worked in this space knows to be true: postpartum mental health distress rarely arrives with a label.
It arrives as exhaustion. As “I’m not sure I’m doing this right.”
As a question about supply, pumping, whether it’s okay to feel this disconnected from something you were supposed to love immediately.
Willow integrated Ema, AI built for women’s health, with the goal of closing the maternal care and data gap.
The pattern mentioned above appears consistently in Ema’s conversational data through the Willow app.
A mother reports mastitis symptoms.
Ema walks her through the clinical presentation, confirms she should keep pumping, and then she questions if she is using her pump correctly. In the same thread, within a few exchanges, she says she’s “feeling too sad.” Then: “I don’t know. I think I’m depressed. I am not enjoying my postpartum.”
She did not come to the app to talk about her mental health.
She came about a breast infection. The mental health disclosure came through the already-opened door.
The Weight Underneath the Technical Question
New motherhood involves an enormous amount of problem-solving at a time when cognitive and emotional reserves are depleted. The pump has to work. The baby has to eat. The body has to recover.
Work comes back. Sleep doesn’t. Feeding their babies requires skill, and the learning curve sits atop it all.
What Ema’s conversation data shows is that the emotional load of navigating these challenges is not separate from mental health. It is mental health.
When a mother writes, “I’m postpartum and overwhelmed and tired,” and then, in the same breath, asks about flange sizing, she is telling us what the postpartum experience actually feels like from the inside.
The technical question and the emotional state are one and the same.
Breastfeeding carries particular weight here.
The desire to breastfeed, the guilt when it doesn’t go as planned, and the identity questions that come with feeding choices are not peripheral to the postpartum mental health conversation.
In our conversations, women navigating supply concerns often reveal deeper anxieties: about whether they are good mothers, whether their bodies are “working,” and whether the difficulty they are experiencing means something about them.
These are the signals worth asking about.
What Screening Looks Like in Practice
Ema is trained on the Edinburgh Postnatal Depression Scale and is equipped to offer the EPDS when a conversation warrants it.
The value is being present for the moment when a woman is ready to name what she’s feeling.
That moment rarely comes as a direct request for mental health support. It comes when someone is already in a conversation about something else, and something shifts.
A woman dealing with mastitis says she feels sad. A woman worried about supply says she doesn’t feel like herself. A woman managing the logistics of going back to work with a wearable pump says she’s not sure she can keep up with it all — and the “it all” isn’t about the pump.
Ema is designed to hear that. She doesn’t stay on the clinical or technical track when the conversation moves. She follows the person.
And when the moment is right, she offers the screening as a natural next step.
In one exchange, a woman was offered the EPDS after disclosing depressive feelings. She declined.
Ema acknowledged that and asked if she wanted to talk about something else. That’s the right response. The offer was made without pressure. The door stays open.
Sometimes what matters most is that someone asked at all.
The Continuity Problem
One of the most persistent structural failures in maternal mental health care is fragmentation.
A woman sees her OB at six weeks postpartum for a brief screening. She may get a call from a nurse. She may be given a referral she never follows up on because she doesn’t have the capacity to navigate a new care relationship while managing a newborn.
The clinical touchpoints are too few, too far apart, and too often siloed from one another.
The postpartum period lasts far longer than the six-week checkup implies. Mental health symptoms can emerge weeks or months after delivery, shift in character over time, and interact with physical challenges in ways that don’t fit neatly into any single provider’s lane.
A lactation concern becomes an anxiety spiral. A supply drop triggers a grief response. A difficult return to work surfaces a postpartum depression that wasn’t fully recognized at six weeks.
Ema sits inside these moments because she’s embedded in the platform women are already using. She doesn’t require a separate appointment, a referral, or the cognitive bandwidth to seek out a new resource.
She’s in the Willow app that mom is already using multiple times a day to manage her pump.
When Ema identifies a woman who may need more support than she can provide, she routes to the right resource — whether that’s a SimpliFed lactation consultant for feeding-related concerns or a clinical professional for mental health follow-up.
The conversation leads to the handoff with someone who can do more.
What the Month of May Means for the Rest of the Year
Maternal Mental Health Month is a useful moment of attention. The awareness campaigns, the social media posts, and the statistics shared in newsletters matter.
But the gap in postpartum mental health care is not really an awareness problem.
Most people in the perinatal space and beyond know the statistics. The problem is access, timing, and continuity.
AI doesn’t close that gap on its own.
What it can do is be present in the spaces where women already are, at the times when they need something, and attentive enough to recognise that a conversation about a pump, a clogged duct, or a supply concern is also a conversation about how someone is doing.
The question behind the question is often the more important one.
For Willow, the conversation data Ema generates is a map of where mothers are struggling, what they reach for when they need help, and when they are ready to say more than they came to say.
That information, used well, shapes better resources, better onboarding, and a more connected experience across the full arc of the postpartum year and beyond.
Building the infrastructure to support maternal mental health is a year-round project.
Willow is doing one part of that, and the conversations happening on the Willow platform every day are evidence that women want support that meets them where they are… in their app, in their moment, without having to ask for it twice.
About the authors
Morgan Rose is Chief Science Officer at Ema, an AI platform for women’s health. Ema partners with healthcare organisations and femtech companies to deliver clinically grounded AI support across the perinatal journey.
Lauren Scocozza is the Vice President of Product at Willow Innovations, Inc. For women by women, Willow is building a maternal care platform to address the interconnected challenges of postpartum.
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