There are reasons that laying on your left side is helpful in pregnancy. Most women (but not all) will have a lower blood pressure while lying on their left side compared to when lying on their right side. But with fetal positioning will lying on one's left help the baby's back to come over to the left, too? Two articles help answer the question of whether you should try and sleep on your left side to help your baby turn anterior.
Matsuo, Koji. Maternal positioning and fetal positioning in uteroJournal of Obstetrics and Gynaecology Research Volume 33 Issue 3, Pages 279 – 282 2007
Purpose: ...little is understood about the physiology of maternal–fetal positioning during pregnancy. It was hypothesized that fetal left occiput positioning is affected by maternal positioning. The present study was designed to investigate the relationship between maternal positioning in late pregnancy and fetal positioning in utero.
Methods: A prospective cohort study was conducted at Ueda Hospital, Kobe, Japan. Eligible women were limited to low-risk pregnancies ending in spontaneous vaginal delivery with singleton vertex fetuses. Information obtained from the mother included the preference of positioning during sleep in the second half of pregnancy. Fetal information recorded after delivery included fetal positioning.
Results: Eighty-one (50.6%) of 160 evaluated women preferred left lateral positioning while 70 (43.8%) women preferred right lateral positioning in the second half of pregnancy. Seventy-seven (51.7%) of 149 evaluated fetuses were in the left occiput position while 72 (48.3%) fetuses were in the right occiput position in utero. Maternal left lateral positioning with fetal left occiput position in utero was the predominant positioning (41 of 149, 27.5%). However, there was no statistical relationship between maternal positioning and fetal occiput positioning in utero.
Conclusion: More women prefer the left lateral position during the second half of pregnancy. More fetuses are in the left occiput in utero during the late stage of pregnancy. However, no statistical relationship was observed between maternal and fetal positioning.
Maternal positioning and fetal positioning in utero.
Gail's comments on the Matsuo study.
This study explored whether a pregnant woman who sleeps on her left is more likely to carry a fetus whose back is also on the mother's left (left occiput). It didn't look at anterior vs. posterior. It didn't look at how the women slept in the 2nd trimester which may be a bit more to the point. And it certainly didn't look at body balancing.
Again, there is a spectrum of ease to difficulty in helping a baby into position for an easier birth. Maternal positioning as a lone variable separates the position of the mother from the position of her womb.
Women have often told me their baby lays on the left when they wake from a night of sleeping on their left only to find baby back on the right after being upright for a few hours. When one of my own mothers tells me this, I can check the head position to see if the baby has truly changed position or simply shifted weight. If you have read very far into Spinning Babies, you can see that I don't stop with maternal positioning.
Remember the neck? Our necks bend. Gravity can pull the baby towards the mattress while the mother rests, but its likely to be the body of the baby settling down. When mother wakes up and begins walking around, moving around in a vertical position, the baby settles into the position that matches their head more readily, as they are able. If the feet kick on the same side as before, the baby hasn't really changed position.
A posterior baby can kick on the opposite side when the back shifts even a small bit, but without changing out of the posterior position. This is because a small turn can move the location of the feet without effectively rotating the back.
But if the back is readily felt through the mother's abdomen, the back is clearly towards the front, or, the back is generously on one side or the other and the feet then kick far to one side or the other (always opposite the back) then their may be a change in the fetal head position, too.
What about the baby on the right? Is there a clear reason, like a twin on the left (hello!) or a placenta on the front left, a uterine septum dividing the womb, etc. etc.? No?
The baby on the right is there because the womb keeps the baby there. The womb itself is being held in a tip, twist or grip that reduces the available room for the baby to rest on the mother's left. There are no major internal organs on the left, there is a firm liver on the right. The baby is more likely to have an extended head, that doesn't stay comfortable at the end of pregnancy. To be anterior on the right the baby must press her face into the mother's descending colon which fills and empties everyday giving the baby a rumbling shifting pillow. The baby would move if she could. I do believe this.
I've seen over and over, that when the mother has some significant body work her baby will shift from what's been a persistent right sided lie to the left as her broad ligament, her symphysis pubis joint and/or her round ligaments are in order. Sometimes this happens before pregnancy. Then its dramatic, to me, anyway. But the midwife or physician must look for the cephalic prominence to be on the right of the mother's midline before we are sure the baby switched position and will likely stay until labor brings the baby lower and the rotation of birth moves teh baby more and more anterior.
Which side to lay on in labor?
There have been a few studies on maternal position in labor effects fetal presentation. These studies explore whether lying on the same side of the fetal occiput helps baby rotate or lying on the opposite side as the baby's occiput helps rotation.
A study favoring lying on the same side as the fetal occiput (back of the head):
Zhonghua Fu Chan Ke Za Zhi. 2001 Aug;36(8):468-9.
Correction of occipito-posterior by maternal postures during the process of labor
[Article in Chinese]
OBJECTIVE: To investigate the effect on correction of occipito-posterior (OP) by changing maternal posture during labor.
METHODS: One hundred normal primigravida with head OP position in the latent phase of labor were randomly divided into 2 groups:
Group A (n = 50), women were instructed to lay on the same lateral posture with the fetal spine during labor in order to correct the fetal position from OP to occipito anterior (OA);
Group B (n = 50) lay on the opposite side to the fetal spine.
The OP position was diagnosed by vaginal examination or B ultrasound, and the course of labor and mode of delivery were observed.
RESULTS: Thirty-four women delivered vaginally (68%) in group A, with 27 of them turned to OA position (54%); spontaneously
while there were 22 who delivered vaginally (44%) in group B (opposite the fetal spine) and 12 babies who rotated to OA position spontaneously (24%) in group B, a significant difference was shown (P < 0.005).
The average time interval for the 1st stage was (13.5 +/- 6.5) hour and (17.1 +/- 7.2) hour for group A and B respectively, also a significant difference was noted (P < 0.01).
CONCLUSION: To instruct women in labor to take the lateral recumbent position with the same side of fetal spine for correcting OP to OA is an effective method. It may increase vaginal deliveries and shorten the first stage of labor, thus reduce dystocia due to OP position. This method is simple and effective, and maybe adopted in most obstetric units.
This seems to be a fair division of women into two groups. All women were first time mothers (primigravida) with babies who faced the front (so the occiput is posterior).
In this study, laying on the same side as the baby's back is on seems to be more effective than laying with the back up, opposite the side that the mother is lying on.
The Wu study agrees with Ou, studying the same thing 5-years before Wu:
Zhonghua Fu Chan Ke Za Zhi. 1997 Jun;32(6):329-32.
Correction of occipito-posterior position by maternal posture during the process of labor
Guangzhou Second People's Hospital.
OBJECTIVE: To investigate the effect on correction of occipito-posterior (OP) presentation by changing maternal posture during labor.
METHOD: A prospective study was conducted in 120 pregnant women from March 1994 to December 1995. Women in labor were instructed to take the lateral posture so that the resultant force of the gravity of the fetus, the buoyancy of amniotic fluid, and the intermittent uterine contraction may change the fetal position from occipito-posterior into occipito-anterior (OA) presentation. Another 120 women were selected as controls.
RESULTS: (1) In the study group, 106 women (88.3%) delivered vaginally with fetal presentation changed from OP into OA, and 14 (11.7%) received cesarean section. In the control group, only 20 women (16.7%) delivered vaginally, and 100 (83.3%) had cesarean sections (P < 0.001). (2) The average time interval in the study group was 302.6 min for the first stage and 59.8 min for the second stage, whereas 483.7 min and 156.1 min respectively in the controls. A significant difference was noted (P < 0.01).
CONCLUSION:It is an effective method for the mother to take the lateral posture on the same side of the fetal spine for correcting the OP position. The incidence of dystocia may be reduced as well as the cesarean section rate. The method in simple and effective, and can be used in most of hospitals.
Another Chinese study seems to pay attention to multiple factors. Its a little old now, but they still found what they found. Studies since then on this topic have come up with mixed results. That's why we can't take one study too much to heart, but I like that this study adds some other information about the baby's head and the baby's back:
Zhonghua Fu Chan Ke Za Zhi. 1993 Sep;28(9):517-9, 567.
Changing fetal position through maternal posture[Article in Chinese]
The fetal position of 249 cases in their late pregnancy was detected by ultrasound. The results showed that the position of fetal spine tended to lie on the same side as mother's posture during bedrest just before examination.
Fetal posterior or transverse spinal position was prone to occur when mother was on her supine position.
The fetal cephalic presentation did not correspond entirely with the fetal spinal position.
Eighty of the 249 cases presenting fetal spinal posterior or transverse position were chosen at random and corrected by Sims' or hand-knee posture. The better results were obtained especially by the latter. The success rate of correction by maternal posture was affected by the engagement of fetal head and the volume of amniotic fluid. The mechanism of hand-knee posture was discussed. The result indicated that maternal posturing is a clinically valuable procedure. It may be done during pregnancy or in labor to prevent fetal malpresentation.
Gail's comments on Zhao's article:
Though this is a small number of mothers, we find some useful information here.
Zhoa and Shan are also precise in that they note the baby's position "tended to lie on the same side as mother's posture during bedrest just before examination." They realize that the baby's position may well vary at other times in the mother's day. But does this mean the head rotates, too?
Here, we see validation that lying on one's back increases posterior position, but here again, the left or right transverse position is not differentiated.
I'm very excited to see in the literature that the head position (cephalic presentation) was seen to not always go comfortably with the spine. In other words, babies do look over their shoulders and at times, a particular baby may look over its back. Which of these they were is not told here in the Abstract.
Hands and Knees position was found to be more helpful than lying on one's side (Sims'). They conclude that maternal positioning is useful in labor, both side-lying and Hands-Knees, but especially Hands-Knees position.
See Kariminia for discussion of hands and knees in late pregnancy as a tool for correcting OP presentation. Its not favorable, but the study has its weak points. Again, more than hands and knees is necessary for most women.