Red raspberry leaf, otherwise known as rubus idaeus, has been used medicinally since the sixth century. Its use and reputation as an aid in pregnancy and childbirth has grown throughout the years, despite the paucity of research into its safety and efficacy for mothers and babies during pregnancy and birth.
A herb, red raspberry leaf is consumed in tea, tablet or tincture form by pregnant women in the hope that it will make labour easier or shorter. Herbalists throughout the years have claimed that raspberry leaf’s benefits include relieving nausea, period pains and afterbirth pains and preventing bleeding gums and haemorrhoids. Some researchers suggest that it may both stimulate and facilitate labour. Other benefits are reported to be that it is a rich source of calcium, magnesium, vitamins B1, B3 and E, and it may increase breastmilk flow.(2) Much of this information has been anecdotal and the paucity of research prevents any substantial evidence to support these statements. Women, however, continue to take raspberry leaf; various studies show between seven and 58 per cent of pregnant women consume the herb.(3) It is recommended to pregnant women by midwives, obstetricians, friends and the media(4), including the internet. It is freely available in Australian health food shops, supermarkets, pharmacies, via herbalists and recently now via online herbalist suppliers.
A review of the literature suggests that seven animal(1,5-10) and three human(4,11,12) trials have been performed using raspberry leaf for pregnancy. Despite these studies, very little is known about the active constituents of the herb, let alone how and when in pregnancy it should be taken and at what dose. While some studies indicate it may be safe to use, the limited nature of these studies does not provide a clear answer to the questions of its safety and efficacy.
Animal studies in 1941 by Burn and Withell(5) found that an intravenous injection of raspberry leaf extract had a relaxant effect on the uterine muscle of anaesthetised, non-pregnant cats and rabbits. As well as a slight rise in blood pressure, they also discovered a by-product in raspberry leaf tea that not only reduced the strength and frequency of contractions, but also caused tonically contracted muscles to relax.
This relaxant effect of raspberry leaf was suggested by Bamford and colleagues in 1970(6) to ‘modify the course of labour favourably to produce more coordinated uterine contractions’. Further studies similar to these earlier experiments were performed on animal and human extracted pregnant and non-pregnant uteri strips, with most supporting the relaxant effect.
The active ingredients of raspberry leaf could not really be identified until 1995, when Patel and colleagues(7) suggested they may be terpenes and or alkaloids.
A recent animal study published in 2009 by Johnson et al (9) randomised 40 nulliparous rats to raspberry leaf 10 mg/kg/day oral treatments from day one of gestation until birth and compared them to three other groups of rats who ingested other substances. The raspberry leaf group showed a statistically significant increase in the length of gestation. Alarmingly, but not significantly, the pregnancy success rate in the raspberry leaf group was less than the control groups. A significant finding in the raspberry leaf group’s offspring (F1) was that they experienced an early puberty. The (F1) group then produced a significant proportion of growth restricted offspring (F2).
The most recent study by Zheng et al in 2010(10) tested the effects of three commercially available forms of raspberry leaf – tea, capsules and ethanol-based tincture – on in vitro contractility of uteri collected from an unspecified number of diethylstilbestrol (DES) treated non-pregnant and also on late-pregnant rats. In pregnant animals, raspberry leaf tea had variable effects on pre-existing oxytocin-induced contractions, sometimes augmenting oxytocin’s effect and sometimes causing augmentation followed by inhibition. Pretreatment with tea did not alter the ability of oxytocin to initiate contractions. The tea appeared to be more effective than the tablets or tincture.
In 1941, Whitehouse(11) inserted an intrauterine bag to obtain and record the effect of 20 to 40 g of raspberry leaf extract (fragarine) on afterpains on only three postpartum women. There were no controls. The main effect observed was that uterine contractions diminished in frequency and strength and secondary contractions were diminished. Contrary to an earlier study by Burn and Withell5 on pregnant cats, a slight fall in systolic blood pressure was observed. Apart from the 1941 study, there have been no other clinical trials published.
The absence of good clinical evidence surprised and inspired a small group of midwives, including the author (Parsons, Simpson et al 1998), who had cared for many women who were recommended raspberry leaf in pregnancy by obstetricians and midwives attending the study hospital, to conduct a retrospective observational study. The study involved 109 postnatal women. Fifty-eight women consumed raspberry leaf in a variety of forms: tea, tablets and tincture at various dosages, commencing as early as eight weeks and as late as 39 weeks gestation. They were compared to a group of 51 postnatal women who didn’t take raspberry leaf. They were of comparable parity, ethnicity, type of antenatal care, weight and age. There were no preterm births in the raspberry leaf group, in fact, they were more likely to birth on time. The test group were also more likely to have an unassisted vaginal birth and less likely to have artificial rupture of membranes and caesarean delivery. Both groups had similar outcomes for admissions to the nursery, meconium liquor and Apgar scores. Qualitative data received from the treatment group indicated that they were advised to take the herb by various contacts including obstetricians and midwives. They generally perceived that raspberry leaf shortened their labour and they would not only take it in future pregnancies but they would also recommend it to friends.
While the retrospective design of the observational study had limitations, it satisfied the ethics committee sufficiently to allow the Simpson and Parsons team, including a supervising obstetrician, to conduct a double blind placebo-based trial.(12) It involved 192 low-risk, nulliparous women, 96 taking raspberry leaf tablets 2.4 g/day from 32 weeks gestation until birth and 96 taking placebo. Both groups were comparable in all variables regarding safety and efficacy, except there was a slightly less instrumental rate within the treatment group, 19.3 per cent versus 30.4 per cent control group. There were no statistically significant results, but we concluded that further studies with a higher dose are needed before we can draw any conclusions regarding its safety and efficacy.
You would not be alone if, after ploughing through the literature presented, you were feeling somewhat confused. Most of the animal studies involve cadaver uteri infused with raspberry leaf, which is hardly comparable to how women actually consume it in pregnancy. Some studies suggest that the herb initiated contractions(5,1,10) while others said it inhibited them.(6,7,8) One study said raspberry leaf raised blood pressure(5), another said it lowered it.(11) The discrepancies between the studies may simply be a result of varying experimental design and different preparations of raspberry leaf used.
More recent animal studies, such as Johnson and colleagues 2009(9), raised some concerns regarding raspberry leaf. The increased stillbirth rate (while not statistically significant) accompanied by an early puberty in the raspberry leaf group’s offspring and then growth restriction in their subsequent offspring is of some concern. However, it is reassuring that the overall dose they used in rats (10 mg/kg) was significantly less than the dose we used in our randomised trial (400 mg/kg for a 60 kg woman) and we know that the dose 2.4 g/day didn’t produce any statistically significant results.11 Maybe raspberry leaf is more suitable and perhaps safer for humans than rats!
The conclusion from all of this is that it is beyond doubt that more clinical trials using varying doses and forms of raspberry leaf taken at various gestations are needed to provide more information regarding its safety and efficacy. Studies looking at the active constituents are also necessary. Women, however, will continue to take it. Meanwhile, should we as health professionals discourage the consumption of raspberry leaf in pregnancy? I’ll leave that decision to you. I have been conducting a midwifery-led antenatal clinic for the last 13 years and the majority of the women I care for consume raspberry leaf during their third trimester in various forms and in doses generally higher than the dose used in the randomised trial. Most of the women say they get their information about raspberry leaf from the internet or antenatal classes or they took it in a previous pregnancy. To date, I have not seen any adverse effects in either mothers or babies that I can attribute to raspberry leaf. Personally, I took raspberry leaf tincture during my pregnancies and births. I was in my late 30s. After very well, term pregnancies, easy labours and births and two very healthy children, I am grateful that I knew about raspberry leaf. I would, however, discourage its use, until further studies can demonstrate its safety and efficacy. I remain cautious when discussing its use with women and encourage other pregnancy care providers to do the same. Would I do another study? Like many researchers, my dedicated colleague and I are still recovering from the multiple ethics submissions and countless hours and worry we endured during the last two studies, so maybe not so soon. I would, however, be happy to advise and encourage anyone who is interested!
Originally published by O & G Magazine, Vol 12 No 4, Summer 2010. Pages 54-55. Reproduced with permission.