Yes, labor can start while sleeping. In fact, it is more likely to occur while sleeping than when fully awake. Moreover, labor can start at just any time, and most are spontaneous.
The phenomenon of labor, a remarkable physiological event culminating in the birth of a new life, remains an essential juncture in the journey of human existence.
Labor, fundamentally, signifies the termination of gestation and the initiation of giving birth. This complex process involves an interplay of hormonal fluctuations, uterine contractions, and cervical changes, collectively choreographed to facilitate the emergence of the fetus into the extrauterine environment – which is the outside world.
The evolutionary perspective accentuates the pivotal role of labor in species survival. Over eons, mammalian species, including humans, have evolved mechanisms to ensure the optimal gestational period while averting the detrimental consequences of prolonged intrauterine development.
How or why labor starts?
The instigation of labor is an intricate interplay of different molecular signaling pathways. Hormones such as cortisol, prostaglandins, and oxytocin assume central roles in orchestrating the physiological processes underpinning labor.
Notably, oxytocin’s augmentation stimulates uterine contractions and promotes cervical dilation—a coordinated effort to propel the fetus toward the birth canal. In fact, this hormone is also used to induce labor artificially.
Oxytocin is readily available and plays roles in mental health, breast milk production, brain, emotional health, and more.
Genetics also has a substantial say over the onset and progression of labor. Genetic predispositions influence the sensitivity of uterine cells to hormonal cues, thereby impacting the timing and duration of labor.
Labor is painful. Pain serves as a communicative signal, indicating the imminent transition from pregnancy to birth.
When is the labor most likely to start?
As mentioned, that labor may begin at any moment and is often spontaneous. That is why even births outside the hospitals are not rare. This is why deliveries often occur when unexpected, and people often have to call emergency services.
Nevertheless, it is no secret that in developed nations like the EU nations and the US, most births these days occur in clinics. It means that despite its spontaneity, it is a highly predictable phenomenon.
In most cases, doctors can predict when to expect labor or on what day, though they cannot predict the exact time. Such a precise prediction has become possible due to an accumulation of extensive data over the years.
Millions of women give birth in clinics or in well-controlled conditions every year. All the details of the birth process are noted or documented. Hence, it is not difficult to find when most births occur.
Perhaps the most extensive study to date was done in the UK when researchers analyzed the data from more than 5 million births that took place in NHS maternity units between 2005 to 20241.
The above study was so extensive that it provided some sound findings and reliable results. It found that more than half of all births started spontaneously!
Not only that, they also found that just about 28.5% of births occurred during the day, between 9 am to 5 pm on weekdays.
The study found that 71.5% of births occur between 5 pm and 9 am or on weekends! More than half of all spontaneous births occurred between 1 am and 6:59 am.
So, well, this study clearly shows that the majority of births occur at night, and a significant number of labor pains start spontaneously and while sleeping. There is more than a 25% chance that the labor would start while sleeping in any given case.
There is more than a 70% chance that labor pain would begin in the evening or late at night.
Why does labor start while sleeping?
Well, this is a topic of much discussion. It appears that there could be multiple reasons for this.
Perhaps one of the significant reasons is that humans have evolved to give birth at night when things are relatively calm and when they are not busy with other activities. It seems that nighttime just offers better conditions for giving birth.
Another reason is the circadian rhythm. Certain changes occur in the body during the night, which is better for giving birth.
During the night, there is diminished physical activity, calmness, low blood pressure, body temperature, and so on. There are fewer external stimuli, and thus the body can focus on giving birth.
Of course, there are hormonal reasons, too. Oxytocin, often called the “love hormone” or “bonding hormone,” is a central player in labor initiation. Its secretion is intricately tied to circadian patterns, with levels typically peaking during the evening and early hours of the night2.
This hormonal surge is not only associated with uterine contractions but also promotes a sense of relaxation and emotional bonding—factors that align seamlessly with the conducive environment late night provides for labor.
Recent studies have also illuminated the role of fetal influences on the timing of labor onset. The fetus, equipped with its own circadian rhythms, communicates with the mother’s body through intricate hormonal dialogues3.
This synchronization between maternal and fetal circadian clocks could potentially contribute to the nocturnal preference of labor initiation. As the fetus’s hormonal signals align with the mother’s nighttime hormone surges, the threshold for labor initiation might be surpassed more frequently during these hours.
The bottom line
Although not entirely understood, the phenomenon of late night labor initiation finds its roots in the intricate interplay of chronobiological rhythms, hormonal fluctuations, and evolutionary adaptations.
The synchronization of maternal and fetal circadian clocks and the conducive conditions provided by the nocturnal environment collectively contribute to the preference for labor to begin during the late night hours.
All this means there is a high chance for pregnant women to experience spontaneous labor while sleeping. The majority of labors start in the evening or at night, and a significant number of them after 1 am, while sleeping.
References
- Martin P, Cortina-Borja M, Newburn M, et al. Timing of singleton births by onset of labour and mode of birth in NHS maternity units in England, 2005–2014: A study of linked birth registration, birth notification, and hospital episode data. PLOS ONE. 2018;13(6):e0198183. doi:10.1371/journal.pone.0198183
- Roizen J, Luedke CE, Herzog ED, Muglia LJ. Oxytocin in the Circadian Timing of Birth. PLoS ONE. 2007;2(9):e922. doi:10.1371/journal.pone.0000922
- Mendelson CR, Montalbano AP, Gao L. Fetal-to-Maternal Signaling in the Timing of Birth. J Steroid Biochem Mol Biol. 2017;170:19-27. doi:10.1016/j.jsbmb.2016.09.006
Dr. Preet Pal SB is a physician (M.D. Medicine) with a specialization in diabetes (Fellowship in diabetes, Royal Liverpool Academy). He has a particular interest in metabolic disorders, considering that they are rising in every corner of the world, more so in India.