Pregnant women who find their babies move little in the evening are much more at risk of stillbirth - prompting a midwife researcher's call for vigilance.
"Some women put off contacting their midwife in the evening as they think it's inconvenient and don't want to seem over-anxious," Wellington midwife and University of Auckland PhD student Billie Bradford said.
"But, delays in women presenting with fetal movement concerns have been linked to complications, including stillbirth, in other studies."
A study just published by Bradford showed how women who reported their babies were "quiet" in the evening, with light or no movement, had an almost four times' greater risk of stillbirth compared to women with nocturnally active babies.
Bradford said while all babies had some quiet times and some active times, the evening was normally an active time, so if the baby didn't have moderate or strong movements at that time like they normally would, a check-up was needed.
In most cases, this would provide reassurance that the baby was doing okay, she said, although some women may need a follow-up scan or closer monitoring.
Stillbirth is defined as the loss of a baby after 20 weeks of pregnancy, and many stillbirths are thought to be preventable.
An estimated 2.64 million babies die before birth globally each year, including around 300 babies in New Zealand.
About one in every 500 women in New Zealand will experience a late stillbirth, losing her baby at or after 28 weeks of pregnancy.
"Stillbirth is incredibly traumatic for families, and we felt there was potential to prevent some stillbirths if fetal movement was better understood," Bradford said.
"We knew from other studies that women felt more movements in the evening, but we weren't sure how relevant this was to stillbirth."
Researchers interviewed 164 women who had recently experienced a late stillbirth and asked them what their baby's movements had been like in the two weeks before the baby died.
Around half of those women had lost their baby at 37 weeks or later.
For each stillbirth, three or four women at the same stage of pregnancy and from the same part of the country were also interviewed.
Responses were then analysed to see what was different in the pregnancies where the baby had died, compared to the ongoing pregnancies.
The findings, published in the high-ranking journal Scientific Reports, confirmed that decreased frequency and decreased strength of baby movements were linked to stillbirth.
Most strikingly, for babies who had quiet or light movement in the evening, stillbirth risk increased by nearly fourfold (3.82 times).
"The good news for pregnant women is that feeling moderate or strong fetal movements in the evening is very reassuring of a healthy baby," Bradford said.
"Feeling groups of strong movements and baby hiccups is also a good sign."
A recent study by the same team described a "new normal" for baby movements: a 24-hour pattern in which babies are more active in the evening and at bedtime, with movements often getting stronger as babies come to term.
Senior author, University of Auckland Professor Lesley McCowan, said the latest findings raise the question of whether fetal movement screening and monitoring in tune with babies' 24-hour pattern of activity might help prevent stillbirths.
"Medical researchers are looking at ways to improve treatment outcomes in many areas by taking into account circadian rhythms," McCowan said.
"A ground-breaking 2017 study found that open heart surgery was more successful when it was conducted in the afternoon instead of the morning, all other things being equal, due to syncing with circadian rhythms.
"We need more studies to investigate whether evening fetal movement screening and assessment may help prevent stillbirths."
The research team, which also included a researcher from the university-based Liggins Institute, was now looking at fetal movement patterns in women at raised risk for stillbirth, such as women with obesity and women whose babies are not growing well in the womb.
For now, Bradford said, the message for pregnant women was clear.
"We advise pregnant women to trust their gut, if they really feel something is wrong with their baby's movements, get a check-up, it may make all the difference."