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How long is a pregnancy without medical intervention?

newborn baby being examined at the hospital

I have discussed in my previous posts various methods that have been more or less scientifically proven to potentially induce labor. We have talked about eating dates, drinking raspberry leaf tea, and evening primrose oil. We have also discussed the "birthing kick" (i.e., having sex to induce labor) and the dreaded labor cocktail. Pros and cons, evidence or not.

Now I have reached the eternal question: How long is a pregnancy?

What is the optimal timing for delivery? For the woman? For the baby? Does it matter how your mother or sisters gave birth?

In Sweden, a normal pregnancy is considered full-term at 39 weeks and 6 days. A normal Norwegian pregnancy is a few days longer. It may seem a bit strange.

Is one actually pregnant for a longer duration in Norway? The answer is no.

It's because different scales are used in the early ultrasound examination (dating). Nothing else. So, it's not really the case that a Norwegian pregnancy is actually longer.

How long is a pregnancy - From 43+ weeks to 42+0 weeks

In my clinical practice, I meet many pregnant women who have a desire to be induced, i.e., to have their labor medically assisted and initiated.

We must remember that towards the end of pregnancy, almost all women are tired. They are tired of not being able to sleep, tired of being in pain, and tired of having to get up and pee multiple times at night. Some are worried that something might happen to the baby.

Simply put, they want the baby to come. Now!

But when is the most optimal time? What does science say? I have pondered this and now want to share some evidence-based facts (studies) on this constant question I often receive.

To begin with, when I was the youngest, smallest resident at the clinic many years ago, women would go a maximum of 3 weeks past their due date. It was not uncommon to give birth in week 43 or beyond. I don't think waiting longer than that has ever been accepted.

Then something happened, and the accepted timeframe became, or rather was, 42+0 weeks of pregnancy. Studies show that waiting beyond 42 weeks does not lead to any better outcomes, while the risks of something happening to the baby increase.

The SWEPIS Study

The SWEPIS study was a Swedish multicenter study conducted at 14 out of Sweden's 47 delivery clinics from 2016 to 2018, including SÖS.

The SWEPIS study examined whether induction of labor at 41 weeks + 0-2 days resulted in better outcomes for the newborn compared to expectant management and induction at 42 weeks + 0-1 day.

The outcome was a composite variable that included stillbirth, neonatal death, and morbidity. The reason for combining them is that the outcome is so rare.

The researchers estimated that they needed 10,038 participating women to test the hypothesis and identify a clinically relevant difference between the groups with sufficient probability. After recruiting 2,762 women (28 percent of the intended number), preliminary analyses were conducted.

When the researchers examined the deaths that had occurred, they found that none had occurred in the group induced at 41 weeks (0.0 percent; 0/1,381) compared to six perinatal deaths (0.4 percent, 6/1,379) in the control group (42 weeks).

As a result, the researchers recommended prematurely terminating the study for ethical reasons. The study was discontinued in October 2018, and the results were published in November 2019.

The authors concluded that the study's results should be interpreted with caution but also recommended that women be offered induction no later than 41 weeks throughout Sweden.

woman during ultra sound

Criticism of SWEPIS

SWEPIS has been loudly criticized by the rest of the research community. The criticisms include not recruiting the number of women initially deemed necessary and not demonstrating any statistical difference between the groups in the primary outcome.

Despite this, it was recommended for ethical reasons to close the study. It should be noted that the mortality rate in the control group was surprisingly high, much higher than "normal" Swedish figures. Furthermore, the deaths occurred in facilities where they deviated from what was supposed to be included in the study, namely routinely conducting ultrasounds at 41+0 weeks to exclude high-risk pregnancies.

Conclusions and recommendations are therefore based on an uncertain foundation, something that has also been pointed out by other researchers in the subsequent sometimes heated discussion.

How should research be communicated?

In connection with the publication of the study results, the study began to receive attention in local and nationwide media, where headlines such as "The birthing unit in Falun changed routines already last spring. Senior physician: We couldn't wait" could be read.

SWEPIS has been described in the media without nuance and without reflecting the criticism and parallel scientific discussion that actually followed the publication. The attention has led to increased pressure on maternity clinics in the country, the pressure that has forced them to justify why they have not yet changed their routines and offer induction at 41+0 weeks to everyone.

My opinion on when to terminate a pregnancy

To recommend that everyone should be induced no later than 41+0 weeks undoubtedly leads to more inductions and extended healthcare durations. If this is not included in the clinics' planning and no new resources are provided, a change in routines will occur at the expense of something else. Unfortunately, that is the harsh reality.

It could, for example, involve deprioritizing other patient groups or the healthcare professionals' working environment. We all remember what happened afterward. After SWEPIS.

One example is the so-called "midwife crisis."

That is, the working environment at our maternity clinics went completely out of control and led to many midwives resigning. Such consequences should also be taken into account when considering changing routines in such a drastic way as SWEPIS actually did.

Of course, we should not let children die. No one wants that. However, all women should be offered a qualified ultrasound at 41+0 weeks, where high-risk pregnancies should be recommended for induction. Just as they do now in Stockholm.

It is very likely that induction after 41 weeks will ultimately prove to result in better outcomes for the baby compared to expectant management and induction after 42 weeks, and I don't oppose that.

However, this type of decision must be preceded by a thorough review of the collective scientific literature. This should then lead to the conclusion, not a dubious result from a study that was conducted at 28% completion and then closed, with many shortcomings.

woman during childbirth

What happened at the clinic after SWEPIS?

In December 2021, the following was published in the Stockholm region:

"According to the guidelines, all women should have given birth or be in labor before gestational week 42+0. At the beginning of week 41, healthcare is recommended to offer the woman induction or a time for assessment..."

In essence, this means that if a woman demands induction at 41+0 weeks, it is difficult for healthcare to resist, even if there is a lack of both available spaces and resources. I wonder when they plan to rectify this. Although, in all fairness, the birth rate is declining, which might save the situation, but still.

"A new SWEPIS"?

The SWEPIS research group then joined forces with a Dutch/Australian research team for another publication. They sought all randomized studies on induction at week 41 or 42 and conducted a so-called meta-analysis. The outcome they studied was the same as in the SWEPIS study, namely fetal death or morbidity.

The Result

In this study, they found (again) that induction at 41 weeks significantly improved neonatal outcomes compared to waiting until 42 weeks, without increasing the rate of cesarean section.

This advantage was only observed in primiparous women, while the occurrence of mortality and morbidity was too low to demonstrate any effect in multiparous women. However, the magnitude of risk reduction is still uncertain.

Women with pregnancies approaching 41 weeks should be informed about this to make an informed choice.

Well, what can one say?

/Dr. Eva


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