I've done a great deal of research (mostly internet) on the effectiveness and safety of using castor oil to bring on labour.  Here is what I've found and what I've concluded from that.  These are my own opinions, but I've tried to give my reasoning for everything.

Castor

oil is a very old method for encouraging labour.  It's been used for centuries.  It has not, however, been extensively studied using modern techniques, so most of what is known about it is anecdotal.  It is unclear how castor oil is supposed to work, but the most popular theory is that it stimulates the intestines and bowels to spasm, and this in turn causes the uterus to spasm and sometimes labour will be started from this.  Another theory is that the laxative effect of the oil causes hormones to be released by the mother, having an effect similar to being induced in hospital.  The last theory is that the diarrhoea caused by the castor oil makes the mum dehydrated, and often dehydration will cause the onset of labour.

Effectiveness

So does it work?  To some degree, yes it does.  I don't think it would have been used for such a long time if it didn't work.  What I do think, though, is that it will not work every time. Based on the results of some small research studies that have been done, women who are past their due date are much more likely to start labour after a single dose of castor oil than those who don't.  I expect that women who are not past their due date and take castor oil will be less likely to start labour, because baby's not ready yet.  Castor oil is not a hormone, but a very effective laxative, and therefore, if the baby is just about ready to come out, a gentle nudge can get things started, but if not, baby will stay put.  This is a theory, and more studies need to be done before we know how effective castor oil really is.

The other thing to consider is that, being a laxative, by trying the castor oil method, a woman will subject herself to an intense cleanout, lasting a few hours.  The potential side effects are dehydration, which can be bad for the baby, and exhaustion, as well as frustration if nothing happens.

Safety

There are a lot of things said about castor oil and its safety.  Here's what I think about each of these things.

• The oil passes to the baby, causing it to pass meconium, and putting it in danger.  After a lot of research, I concluded that this was unlikely, because castor oil is not digested by the mother (it passes straight through the digestive tract), and the only way a baby receives nutrients from the mother is through her blood, then through the wall of the placenta into baby's blood.  Therefore the laxative effect of castor oil is unlikely to act on the baby in the same way.  That's not to say that meconium will not be passed by the baby, but if this were the case it would be because baby is in distress.  If castor oil causes an intense labour, or if baby is overdue, then there is a chance of foetal distress, and therefore meconium stained water.
• Nurses know if you've used castor oil because baby comes out slippery.  None of the castor oil goes any further than the mother's digestive system, so it is impossible for the baby to have oil around it after the birth
• The placenta will slip off the uterus wall because of the oil.  Once again, no oil goes further than the mother's digestive system.
• Baby will be delivered earlier than it is supposed to be.  This one I cannot answer with confidence.  From what I have read, I concluded that baby will not budge unless it is ready to, but I also believe that there are very few reasons to attempt this unless there's a medically good reason.
• The mother can become dehydrated, causing foetal distress.  This is a good possibility, because the castor oil causes diarrhoea, which causes the mother to lose a lot of water.  If she does not increase her fluid intake significantly, she risks dehydration.
• The labour will be more intense.  The only references to this one were anecdotal, and it is unclear how this could be possible.  If castor oil causes the release of hormones in the mother, then it's a possibility that the labour could be similar to an induced labour, but I'm not convinced.  When a woman is induced using hormones, she is attached to a drip for the duration of the labour, and the artificial hormones are fed into her until the baby is born.  Is it possible that castor oil could stimulate such an amount of hormone release in the mother?  I don't know, but I personally doubt it.

 

Conclusions and recommendations

1. Think very carefully about your reasons for wanting to bring on labour.  If you are before your due date, and there are no medical reasons to induce, then don't do it.  Even if you're very uncomfortable, over it, or worried about baby getting too big, these are not medical reasons to try and self-induce.  By the time you're 37 weeks, you've only got a short time to go, so perhaps practice patience, rather than dwelling on when labour is going to start.
2. If you are past your due date, still think carefully about your reasons for inducement.  My own opinion is that castor oil could be tried if you are staring down the barrel of a hospital induction, and you want to try and go into labour before this.
3. If you do decide to try it, do not exceed the doses and times that are recommended by midwives and doctors.  Preferably, try it with your caregiver's knowledge.
4. Do not plan to go anywhere for the day that you choose to do this - it will clean you out very effectively and without warning.
5. Drink a lot of water to reduce the risk of dehydration.

 

Once again, if you are not at or past your due date yet, then there is no selfless reason to try and bring baby on.  Even after the due date has passed, it's a better idea to work with the midwives or doctors to allow the birth to start when it's time, until it is clear that interference is necessary.  Please allow nature to take its course and start labour spontaneously, even if you are heavy and uncomfortable, you like a particular date or you just want it over with.  I am starting to wonder if something chemical happens to a mother who is close to her due date, that causes her to become impatient.  It has happened to me with every one of my pregnancies, and it's something I've had to battle with, to remain patient and stop dwelling on the imminent labour, willing it to start NOW!
 

I am currently 38+2 weeks pregnant, and am fed up.  I want to get on with my life and meet the new little one.  A couple of times, I have thought that labour was about to start, but as yet, these have been false alarms.  I have decided to focus on the due date and stop trying to analyse every little niggle.  Worst case, this pregnancy will be finished in a few more weeks.

I believe that castor oil is not a dangerous thing to do, but it is an unwise thing to try without good reason.