Anxious fathers can make Caesarean operations more painful for mothers, research suggests.
Caesareans have become more popular
Scientists found a woman's level of fear and anxiety about surgery was likely to be raised if their birth partner was anxious too.
This increased their pain levels, potentially affecting recovery, and compromising breastfeeding and bonding with their newborn child.
The UK study features in the journal Psychosomatic Medicine.
One in four babies born in the UK is now delivered by Caesarean section, with many hospitals delivering almost 30% in this way.
The researchers say birth partners should be prepared for the possibility of a caesarean at antenatal classes, and briefed about the procedure in advance if it is decided to go ahead.
The study, carried out by the University of Bath and Imperial College London, focused on 65 women scheduled for an elective Caesarean, of whom 61 had chosen their husband or male partner to be present at the birth.
The women and their birth partners were questioned before, during and after the delivery about their fears, expectations and experiences.
The women were also assessed for their pain levels at different stages of the procedure and immediately afterwards.
Women who had the most negative expectations before the operation experienced the highest levels of post-operative pain.
The study also found that women were most afraid during the application of the nerve block used to numb the lower part of the body, rather than the initial incision.
Researcher Dr Ed Keogh said pain during a Caesarean was usually more controlled than a vaginal delivery, but the process was not painless.
"Whilst it has become a social expectation that birth partners accompany and support mothers during a caesarean delivery, it is unclear what part birth partners play in women's experience of childbirth.
"Whilst some women say that birth partners improve birth experiences, others report less positive outcomes.
"It is not unreasonable for the birth partner to have some feelings of anxiety and fear about the operation they are about to witness.
"Rather than removing them from the operating theatre altogether, it would be better to target the emotional wellbeing of the birth partner to help reduce the anxiety and fear experienced by the mother.
"Since anxiety can increase recovery times, it would be useful to study whether increased maternal fear during the procedure has an impact on mothers, such as longer-term recovery from surgery as well as other related factors such as breast feeding and parent-child bonding."
Professor James Walker, of the Royal College of Obstetricians and Gynaecologists, told the BBC News website that the whole point of having a partner present at a birth was to try to help relax the woman.
He said: "I am not sure you can teach people not to be anxious. A lot of people find the biological aspects of delivery more traumatic than the person giving birth."
He said that if a woman's partner had to be coerced into attending a birth, then maybe it was not a good idea.
However, he added: "If a woman's partner wants to be there to support her, then they are probably the best person to do it."
Sue Macdonald, of the Royal College of Midwives, said: "This report reaffirms the importance of communication between both partners before and during pregnancy, in order that both the woman and her partner feel fully prepared for the reality of birth."