by Dr. Ee Von Ling, ND
Care providers of pregnant people (OB, midwife, nurse and MD) seem to take pride in somehow being able to predict the future of your labour and childbirth. Do they have a special sense or skill set to be able to do this?
They are regular humans just like you and me and they are NOT able to predict very much, if anything at all. But they will have you believe that they can.
Here is a list of the most common things that your pregnancy care provider may try to predict but they cannot possibly know the absolute future:
- When your labour will start. There is no way to know when your labour will start. Not by the size of your pregnant belly. Not if this is your first or second or 5th pregnancy. Not even if they check your cervix at 40 weeks (if you are still pregnant). And yet, we will hear of care providers telling clients that they will have their baby early or go past their due date purely on a personal hunch.
Did you know that medicine and science don’t really understand how labour spontaneously starts? This always blows my mind because we certainly have many methods of artificially starting labour. We just don’t know the exact mechanism that causes your body to start its own labour. We do have some understanding that the baby influences the start of labour, and this makes sense. When your baby is mature enough to survive and thrive outside, their body secretes proteins from their lungs and brain that can eventually make their way into your blood circulatory system and to your brain. In the brain these signals received from the baby trigger the production of different hormones that prepare and perhaps trigger the body to start labour.
Around your due date, your care provider may offer to check your cervix. This check is optional and only gives us a snapshot of what is going on with your pregnancy at that moment. Even if your cervix has changed and is showing signs of getting ready (getting soft, moving from posterior to anterior position, starting to dilate by 1 or 2 cm), we can’t tell when labour will start. Even if your baby is low in your pelvis, there is no way to predict when labour will start.
There is no way to predict when labour will start if this is your first pregnancy or subsequent. Many people hear that first babies come late, and statistically this is somewhat true. According to the US childbirth data available, by 5 days after the due date, 50% of babies of first time parents will be born, and the other 50% are born after this time. What about subsequent babies? By 3 days after the due date, 50% of subsequent babies are born and the rest are born after this time.
What does this mean? We are born procrastinators (you may groan now).
There is no way to predict when labour will start according to family history or within the birthin history of the same person. Each pregnancy is different, and this includes when labour will start. That said, research has been able to find some factors that may increase the chance of preterm labour. Some of those factors are genetic and some of those factors are environmental (for example nutrient deficiencies, illnesses, smoking, drinking alcohol or doing drugs while pregnant).
It may seem harmless to tell a pregnant person that their baby will come early or late. But for that person, such baseless comments can cause unnecessary stress or even cause that person to make pregnancy or childbirth-based decisions that may not be healthy and are certainly not warranted.
- The size of your baby. The only way to get an accurate assessment of your baby’s weight is to weigh the baby after they are born. There is no accurate way to know the exact size of your baby before that. Not by the size of your belly. Not by the amount of weight you have gained. Not by ultrasound assessment.
It is pretty common, although not actually considered a standard part of prenatal care, to be told to get a 3rd trimester ultrasound. The main reasons are to assess the growth of the baby (read: size), amniotic fluid levels and general health of the placenta. Parents will be told, “Your baby is 1234 g”. The care provider might run with this info and say “based on this, your baby will be 4567g at birth. That will be a big baby! You will likely need a c-section”. Then they turn around and leave the room, leaving the pregnant person VERY DISTRAUGHT.
There is a lot to undo here. First, ultrasound weight measurements are very inaccurate, with at least a 15% margin of error. The inaccuracy of ultrasound to measure weight WORSENS as you get closer to the due date, by at least 20% margin of error. There is no other professional industry that would accept such a high margin of error. Could you imagine if an engineer used tools with such a high margin of error? “I think this bridge will be 50 metres long, give or take 10 metres”. Or if your pharmacist said, “The dose of this medication is 100mg give or take 20 mg”. Even with acknowledging the margin of error, it is very hard for parents to “unhear” that they may have a large baby. Thinking that a baby is going to be a certain size most definitely influences medical decisions around early induction and choosing c-section.I have had clients choose a c-section based on “big baby” predictions, only to find out the baby was a very average 7-8 pounds.
Growth in pregnancy is not linear. This means that a snapshot of what is happening now cannot predict what will happen in the future. Weight gain often happens unevenly throughout pregnancy. You or the baby might gain most of your weight during 1 trimester and not as much the next trimester. As long as the placenta is healthy, some babies might be 80 or 90 percentile for weight during much of the pregnancy (according to ultrasounds) and then end up being 50% for their birth weight (real life weight).
Let’s also not underestimate the amazingness that is your body. I have attended births where the parent vaginally birthed (and often without an epidural), 9, 10 and almost 11 pound babies. We just had no idea of the baby’s weight and just focused on her being able to birth her baby.
Don’t get me wrong, ultrasounds can be a useful tool to track trends in a pregnancy. We can track over a series of ultrasounds that a baby is growing well, or not well, or is trending on the upper end of the weight charts. We cannot make such a guess based on just one ultrasound picture. Even so, there will still be surprises at birth. No technology that currently exists is perfect.
Ultrasounds aside, any other comments on a person’s weight related to baby’s size should stop as there is no relationship between the two. In fact, let’s just stop comments on the size of people’s pregnant bodies altogether.
- How long labour will last or how it will progress. When labour starts, your miraculous body is working to eventually accomplish a few things: a) Softening and thinning out the cervix from the firmness of your nose to the stretchiness of a piece of very thin spandex material; b) Drawing open the cervix so that it is fully dilated and “gone; c) shifting the muscles towards the top of the uterus so that they can better move the baby down into the vagina; d) Moving the baby around the pubic born to e) emerge and be born out the opening of the vagina.
There is absolutely no way to accurately predict how long any of these stages will take. Checking the cervix and the station of the baby (how far down they are in relation to a specific point in the pelvis) are a couple of the ways to assess how the labour is progressing. The softening of the cervix (step a) is expressed as a percent with 100% being completely soft and stretchy like a piece of spandex. It takes a lot of work for this to happen and it needs to happen in order for the cervix to open fully. Sometimes the cervix effaces completely first and then the cervix starts to dilate. So if the cervix is only minimally dilated (say only 1 or 2 cm) but it is 100% effaced, that is still a very good sign because the cervix can easily and sometimes quickly dilate to 10cm.
Other times, the cervix softens a little then dilates a little, then softens a little more and so on. So when checked, the cervix may be 4cm (yay!) dilated but 50% effaced (still good, but more work and time may be needed for the cervix to become completely effaced and dilated).
There are also those times when me and the birthing team are completely surprised when all of a sudden the parent goes from 5 cm to fully dilated within an hour.
And while the cervix is changing, the baby is moving downward. The system of assessing this movement is called “stations”. Zero stations means the baby’s head is aligned with a bony landmark within the pelvic called the ischial spines (or simply “spines”). If the baby is higher than this, a negative number is used, like -1 or -2. If the baby is lower than this, it means the baby is descending into the vagina and positive numbers are used + 1, +2 and so on to +5 being the baby’s head is about to be born. In a textbook labour, when the cervix is fully dilated, the baby is at zero station. In real life the cervix can be dilated and the baby is at -2 station (still high), or the cervix can be just 5 cm dilated and the baby is at zero station (quite low).
All this information just illustrates that there are too many factors in play to be able to predict or dictate how fast a labour should progress. Unfortunately a long held “formula” (called Friedman’s curve) is often quoted: “We expect your cervix to dilate 1 cm every hour.” This rate was created by a Dr. Friedman based on his observation of 500 births in first time labouring women aged 20 – 30 years old in the 1950’s. He was the first to put a timeline on labour and his observed rate of dilation in his limited population of study has been used as a guideline ever since. As you can imagine things have greatly changed since the 1950’s and this very limited view of labour can no longer be applied. To read a full and thorough critique of using Friedman’s curve you can read this article by Evidence Based Birth.
The main point here is that there is a huge range of how long a labour may last. As long as the birthing parent and baby are doing OK and as long as there are signs of labour progressing (cervix is changing, baby is descending), then we just need to afford you the time to allow your body work and make childbirth happen.