The length of human pregnancies can naturally vary up to 5 weeks

Science Daily covers a recently published study from journal Human Reproduction, investigating the variability in the length of human pregnancy:

Normally, women are given a date for the likely delivery of their baby that is calculated as 280 days after the onset of their last menstrual period. Yet only four percent of women deliver at 280 days and only 70% deliver within 10 days of their estimated due date, even when the date is calculated with the help of ultrasound.

Already 40 weeks pregnant? Not to worry, that’s within the range of normal! Researchers found that the average length of pregnancy was 328 days, which is 38 weeks and two days, though the length of pregnancies can vary by as much as 37 days.

“We know that length of gestation varies among women, but some part of that variation has always been attributed to errors in the assignment of gestational age. Our measure of length of gestation does not include these sources of error, and yet there is still five weeks of variability. It’s fascinating.”



Pregnancy” by Robert Pecino Martinez is licensed under CC BY 2.0

In addition to variation in gestation length:

Embryos that took longer to implant also took longer from implantation to delivery, and that pregnancies that showed a late progesterone rise were significantly shorter by an average of 12 days than pregnancies with an early rise.

Dr Jukic said: “I am intrigued by the observation that events that occur very early in pregnancy, weeks before a woman even knows she is pregnant, are related to the timing of birth, which occurs months later. I think this suggests that events in early pregnancy may provide a novel pathway for investigating birth outcomes.”

Read the whole story here.

Gestation and the Maya calendar


Maya life revolves around the concept of time. So much so that children are named after the date of which they’re born, and agricultural, civil, religious decisions were derived based on a priest’s reading of sacred calendars. The Maya civilization had a distinctive, complex, and precise calendar system which consisted of more than 20 intercalated counts, or cycles, of differing lengths.

The Tzolk’in, or Sacred Round is a 260 day calendar made up of 20 days of 13 numerical coefficients, and is the central hub of Maya time. The Tzolk’in lists sacred days, omens, sacrificial, warring and agricultural advice. The Haab’ is a 365 day calendar of the solar year. The Haab’, functioning very similar to our own calendar, is made up of 18 named “months” of 20 days each, with a much-dreaded interval of 5 unlucky days tacked onto the end of the Haab’ cycle. The Haab’ combines with the Tzolk’in to create 18,980 different permutations of days, forming the complex 52-year Calendar Round. To calculate periods of time longer than the 52 year cycle of the Calendar Round, the Maya used the Long Count calendar.

From this introduction of Maya time, we can look more closely at one interesting aspect of the Tzolk’in cycleThe key constant of the Maya calendar system is the Tzolk’in 260-day cycle, made up of 20 day names and 13 numerical coefficients.


Representation of the Tzolk’in calendar. The 13 numbers (depicted as the inside circle) combine with each of the 20 day signs (the larger circle), representing the 260 day Tzolk’in cycle.

But what is the significance of 260 days?

The Tzolk’in cycle results in different permutations of the 20 day-signs with a number from 1 to 13. 20 is an important number for Mayan mathematics. Namely, 10 fingers + 10 toes = 20. One-word translations of the 20 day signs are as follows: earth, wind, house, lizard, serpent, death, deer, rabbit, rain, dog, monkey, tooth, staff, jaguar, eagle, owl, quake, knife, storm, and birth. These one-word translations are only sketches of the different meanings of the day-signs, but nonetheless point to an important theme. The 20-day sequence of day signs ends with birth, and illustrates how the Maya concept of time is not only cyclical, but also leads to the development of something new. That the sequence ends with birth lends itself to understanding Maya time as the spiral growth of human and cosmic proportions, beyond the scope of the cycle of a clock.

The Maya conceive of 13 phases of the moon from new to full, which may explain the importance of the number 13 in the Tzolk’in calendric cycle. During a new moon, the moon isn’t visible to the observer until around the second day. Counting forward, the time from new to full moon, or the growth cycle of the moon, takes approximately 13 days. By day 13, the moon appears full for 2 – 3 days. In this way, the number 13 symbolizes the growth of the moon from new to full. While there are alternative interpretations of the number 13, the significance of the number 20 and 13 addressed above introduce one consistency in the Maya worldview: the microcosm (individual)  and macrocosm (universe) mirror each other.

It is possible that the 260-day Tzolk’in cycle originated to predict when a woman would give birth. The length of human gestation is approximately 260 days, from the number of days between first missed period and birth. Therefore, a child conceived on 1 Imix would be born on 1 Imix of the following Tzolk’in year. Interestingly, these those 260 days corresponds to nine lunar cycles of 29.53 days each. That the 20 day signs begin with earth and end in birth support this theory.

The importance of the number 13 has reference to the lunar growth cycle, and the 260-day Tzolk’in calendar is made up of nine lunar cycles of 29.53 days each. The combination of these features is one reason for calling the Tzolk’in calendar a “lunar” calendar. While this explanation of the origin of the Tzolk’in calendar can never be proven, it nonetheless introduces the importance of astronomy for the Maya. Maya goddess, Ix Chel (pronounced Ish-Chel) supports the synthesis of individual with the cosmos, or birth with moon. Ix Chel is considered a woman’s god, and represents birth and medicine. She is also associated with the moon, and has been called “Our Mother Moon“.


Representation of Ix Chel, Maya goddess of childbirth, motherhood, and the moon. Source: Dresden Codex

This brings up another complex idea: the triangular relationship between the earth, moon, and sun. These features further point to the macrocosmic relationship of the earth, moon, and sun in the understanding of the Tzolk’in calendric cycle.

It’s also possible that the 260 day cycle tracked a different sort of fertility: the period from planting to harvest. 260 days corresponds to the time between planting and harvesting certain types of maize, from zenith to zenith. According to creation myths such as the Popol Vuh, as well as Preclassic artistic representations, humankind was fashioned out of maize by the gods. As an agricultural society, maize is the staff of life and survival depends on the production and harvest of maize. In this sense, the life cycle of maize is emblematic of the human lifecycle.

That the Maya combine the Haab’ and the Tzolk’in rounds introduces an important aspect of the Maya worldview. The Haab’ is the calendar of the yearly cycle of the sun, while the sacred Tzolk’in count symbolizes one’s inner dimensions of reality. Combining these two aspects of human experience – the inner with the outer, microcosmic with the macrocosmic – synthesizes the two into one inclusive cosmo-conception. The significance of the numbers 13 and 20, which make up the Tzolk’in count further support the Maya worldview that the inner and outer realms mirror each other. Furthermore, Ix Chel, goddess of childbirth, motherhood, and the moon fully acknowledges the interaction of the individual processes (in this case, birth) with the cosmos (specifically, the moon). Agricultural and gestation explanations for the 260 day Tzolk’in cycle both illustrate how Maya notions of time are tethered to microcosmic and macrocosmic forces. Though the origin of the Tzolk’in 260 day count is unknown, the Tzolk’in has multiple interpretations, and the overlap of these two explanations may explain why 260 days is sacred.

Maya conceptions of time involve an approach of mutual involvement, connection, and overlapping inclusion, rather than a dualistic approach seen in other systems of time. The cycles of growth in the individual mirror those developments in the cosmos, creating a worldview of complete acknowledgement of spirit in matter, and an interconnectedness between self and universe.


The Dresden Codex, one of the surviving folding-screen books of the Maya. Concerned with the 260-day ritual counts. Days are divided up in various ways, with divisions associated with different gods.


Clendinnen, I. (2003). Ambivalent conquests: Maya and Spaniard in Yucatan, 1517-1570. Cambridge [u.a.: Cambridge University Press.

Coe, M. D. (1992). Breaking the Maya code. New York: Thames and Hudson.

Coe, M. D. (1999). The Maya. New York: Thames and Hudson.

Jenkins, J. M. (1994). Tzolkin: Visionary perspectives and calendar studies. Garberville, CA: Borderland Sciences Research Foundation.

What is a doula?

Let’s start with what a doula is not.

Doula ≠ midwife. Unlike a doula, a midwife is a licensed health care provider who attends births and performs clinical tasks such as vaginal exams, perineal massage, and fetal heart rate and blood pressure monitoring. A woman’s midwife, nurse, or physician is responsible for assessing the health and well-being of mom and baby, as well as ensuring the safe delivery of the baby.

A doula does not perform any clinical or medical tasks.

A doula does not diagnose medical conditions or give medical advice to the mother. Under DONA’s code of ethics, a doula encourages the mother to speak with her provider or other nurses, midwives, or doctors when she has questions regarding her health or is looking for recommendations. If a doula gives a recommendation to the mother, it is under the condition that the mother check with her caregiver before acting on the suggestion.

A doula does not make decisions for her client. She doesn’t project her own hopes and values onto the laboring mother, and support the mother regardless of any choice.

A doula does not administer any pharmaceutical or homeopathy medications to the mother.

Rather, a doula provides emotional support for the mother in her labor and delivery. A doula works to cultivate the mother’s breath, focus her energy, find comfortable positions, and relax her through massage, words, and other comfort measures. Throughout history, women have been nourished, cared for, and supported in their deliveries by other women. In artistic representations of laboring women, she is depicted next to two women: the first is a midwife, responsible for the safe passage of the baby, as well as the health of the mother. The second woman by her side comforts the mother, addresses her fears and anxieties, and provides emotional support. Today’s doula is the embodiment of the second woman. She soothes, she mothers the mother.

Today, it is common for women to deliver among strangers. Compared to historic birthing practices where women deliver in the presence of familiar faces, this can produce anxiety and stress for the women which complicates or delays her labor’s progress (see here for more information). Furthermore, many of the birth practices in the West cater to the convenience of the physician, yet make birth more difficult and painful for mothers. Reports addressing the dehumanization of this birthing model have found that the role of a doula – someone who’s only role is to support and nourish the mother – provides numerous benefits to the mother and baby.

This doesn’t mean that partners and other caregivers are less effective in providing continuous emotional support. Unlike the partner or other caregiver, a doula doesn’t have the same intimate knowledge and unique awareness of the mother. A doula is able to relieve some of the pressure often felt by the partner, and allow the partner and other caregiver to support the mother according to their own comfort level. Ideally, a doula and partner use their complementing strengths to support the mother in a richer, more complete way than if either were to support her individually.

The benefits of a doula are supported by research. One Cochrane study by Hodnett et al. (2011) found that women who received continuous emotional support from a doula were:

  • (28%) less likely to have a cesarean section
  • 31% less likely to use synthetic oxytocin to induce or speed up labor
  • 9% less likely to ask for pain medication
  • 34% less likely to rate their birth experience negatively

The same study by Hodnett et al. (2011) found that women who were supported by their social network, without a doula, rated their birth experiences more positively, yet did not impact her use of obstetric intervention.

So, what does a doula do? She provides unique, positive benefits for the care of the laboring woman. Doula work focuses on the art of labor support, and she cultivates skills to comfort, soothe, nourish, and empower the mother. By attending to a woman’s emotional needs, the mother’s obstetric outcomes are improved. When a mother receives continuous emotional support, she is less tense, stressed, and experiences less pain in her labor. Women report more positive birth experiences when supported by a doula, and early mother-infant relationships as well as breastfeeding are enhanced. A doula’s continuous emotional support throughout labor has clinically meaningful benefits for the mother and baby.

Helpful references:

Hodnett ED, Gates S, Hofmeyr G J, Sakala C, Weston J. Continuous support for women during childbirthCochrane Database Syst Rev 2011, Issue 2.

Ina May’s Sphincter Theory

Childbirth Connection’s Best Evidence: Labor Support