Nipple/Areola Dimensions in Early Breastfeeding

Abstract

Background:

Nipple dimensions may be an important factor in breastfeeding (BF) initiation success.

Objective:

To establish standards of nipple/areola dimensions in early BF and to determine whether maternal age, gestational age (GA), parity, cup size, previous BF experience, and early (<2 hours) BF affect nipple dimensions (assessed on the second day of BF).

Design/Methods:

A total of 205 consecutive BF women were enrolled. They were all Caucasians, and had uncomplicated pregnancies, labors, and vertex vaginal deliveries. Measurements (immediately before and after BF) of nipple length and diameter and of prefeeding areolas were by sliding calipers.

Results:

In average, there were no significant differences between right (R) and left (L) side dimensions, except for post-BF nipple length, and post-BF horizontal nipple diameter (significantly higher on the L side). Both R and L nipple length correlated positively with maternal age, gravidity, parity, number of previously breastfed infants, and cumulative number of BF months. Early (<2 hours) first BF did not correlate with increased nipple length. Pre-BF nipple length correlated significantly with post-BF nipple length on both sides. There were significant differences between pre- and post- BF values in terms of nipple length (longer length post-BF), but not in terms of nipple diameter. In stepwise regression analysis, where pre-BF nipple length was the dependent variable, and parity (or maternal age, or previous BF), early first BF, and GA were independent variables, parity, maternal age, gravidity, or previous BF experience were positively and significantly associated with nipple length (p < 0.001). The correlation maternal age-nipple length remained significant in primigravida mothers.

Conclusions:

This study provided a set of standards for nipple and areola dimensions on day 2 of BF in Caucasian women. The only areola/nipple dimension significantly affected by BF is the nipple length. Increasing parity, maternal age, or previous BF experience is significantly associated with increased nipple length.

Introduction

Nipple anatomy may be an important factor in breastfeeding (BF) initiation success. Smith et al., using a real-time ultrasound technique, elegantly showed that the human nipple is highly elastic and elongates during feeding, including ∼2 cm of areola, to form an elongated teat of about twice its resting length.¹ Alexander et al. have estimated that 10% of pregnant women have inverted or nonprotractile nipples, a fact thought to contribute to BF difficulties.² A major textbook on BF³ describes the anatomy of the nipple and the areola and discusses the issues of “flat or “small” or “inverted” or “large” nipples,” but actually provides no numerical figures and no precise definitions.

In contrast, the “breastfeeding handbook for physicians,” second edition, issued as a joint effort of the American Academy of Pediatrics and the American College of Obstetricians and Gynecologists,⁴ states that “nipple size and shape usually do not affect the ability to breast feed,” and mentions that “a woman who has flat or inverted nipples is able to breastfeed if her nipples can become erect.” Thus, it appears that the very definitions of what a flat, an inverted, or a large nipple is, and the prevalence, are not precisely known.

Moreover, very few studies have been conducted on the anthropometry of the breast. We are not aware of any systematic anthropometric studies of the nipple and the areola during lactation, and in particular at its initiation, at a time when nipple dimensions might be critical for the establishment of proper latching, and therefore, for proper initiation of colostrum and milk secretion.

We therefore conducted the following anthropometric study of nipple dimensions assessed on the second day of BF after uncomplicated spontaneous vertex vaginal deliveries. We specifically studied whether maternal age, gestational age (GA), parity, cup size, previous BF experience, and early (<2 hours) BF may affect nipple dimensions.

Methods

The study was approved by our local and the Israeli Ministry of Health Ethics Committees, and written informed consent was obtained from each of the women participating in the study.

Patients

We intended to study ∼200 women who delivered each a healthy singleton infant. We felt this to be important as it is theoretically possible that improper latch for a reason linked to the child (and not the nipple or areola) may affect the nipple or areola dimensions on the second day of BF. Thus, we excluded mothers of preterm (<37 completed weeks of gestation) and of post-term (>41 completed weeks of gestation). GA was calculated from the first day of the last menstrual period, and verified to be consistent within 1 week of early (first trimester) ultrasonographic assessment or by a ±2-week consistency with the Ballard scoring system.⁵

We excluded pregnancy complications such as maternal chronic diseases, pregnancy-induced hypertension, and gestational or pregestational diabetes mellitus. We also excluded women with a history of breast surgery, and those who took medications that may potentially influence latch to the breast, such as antidepressants, anticonvulsants, magnesium sulfate, or opiates. We also excluded two mothers with obviously inverted nipples (concave instead of flat or convex) upon visual inspection of the breast. We also excluded mothers of infants with major congenital malformations, craniofacial malformations, tongue tie of any grade upon visual inspection, and those with 5-minute Apgar scores of <7, facial palsy, respiratory distress, or sepsis.

Anthropometric measurements

All anthropometric measurements took place on the second day after delivery, and were performed by a single individual (G.M.), while the woman was in a sitting position. They were performed twice, immediately before and immediately after BF.

Nipple and areola dimensions were measured using a sliding caliper instrument (Siber-Hegner Maschinen GPM anthropological instruments, Zurich, Switzerland). They were measured to the closest 1.0 mm. Both horizontal and vertical nipple and areola diameters were measured on both sides.

Data collection and statistical analyses

In addition to the anthropometric measurements, we collected and recorded demographic and clinical data from each mother and her medical chart, including the following: maternal age, GA, birthweight, gravity and parity, previous BF experience (both the number of previous children breastfed and the cumulative number of months of BF), early placement at the breast (<2 hours after delivery).

The Minitab version 16 (State College, PA) was used for statistical analyses. Results are expressed as mean ± standard deviation (SD) or n (%). For comparisons of both sides within patients, we used paired t tests for continuous variables, and Fisher's exact tests for discrete variables. We used regression analysis to determine the effect of a given variable upon nipple size, and backward stepwise multiple regression analysis to determine the combined effects of each variable found to affect nipple size at a p-value of at least 0.1 in univariable analysis. A p-value of <0.05 was considered significant.

Results

As stated in the Methods section, the aim of this project was to recruit ∼200 women/infant pairs in the study. After using the inclusion and exclusion criteria determined, 205 women agreed to participate in the study and signed a consent form.

The clinical characteristics of the women/infants pairs are summarized in Table 1, which depicts mean ± SD, and range, or n (%) of maternal age, gravidity, parity, hand dominance, previous lactation experience (cumulative number of months of BF), infant birthweight, and GA.

Table 1.

Clinical Characteristics of the Women/Infants Pairs

Variable	Mean ± SD, and range, or n (%)
Maternal age (years)	29.4 ± 4.8 (18–43)
Gravidity	1.8 ± 1.5 (0–9)
Parity	1.4 ± 1.2 (0–7)
Right-hand dominance	186/202 (92)
Previous lactation experience	151/204 (74)
Previous infants breastfed/woman	1.4 ± 1.3 (0–7)
Cumulative months of BF	10.2 ± 16.3 (0–168)
Infant birthweight (kg)	3.27 ± 0.38 (2.19–4.38)
GA (weeks)	39.3 ± 1.1 (37–41)

BF, breastfeeding; GA, gestational age; SD, standard deviation.

There were significant differences between pre- and postfeeding values in terms of nipple length (p < 0.001), but not in terms of nipple diameter (both vertical and horizontal) (means, SDs, and ranges shown in Table 2). Table 2 shows a comparison of right versus left sides. Although in individual women, there were at times remarkable differences between the right and the left side, in average, there were no significant differences between right and left sides, except for areolar horizontal diameter, postfeeding nipple length, and postfeeding horizontal nipple diameter, which were slightly, but statistically and significantly, higher on the left side than on the right side, in this predominantly right-handed (92%) population of women. However, a comparison of right-handed versus left-handed women showed no differences in any of the nipple or areola measurements.

Table 2.

Anthropometrics of the Areolas and Nipples

Variable	Right	Left	p-value (right vs. left)
Areolar vertical diameter (cm)	5.8 ± 1.3 (3.0 to 9.3)	5.8 ± 1.3 (2.7 to 9.9)	0.630
Areolar horizontal diameter (cm)	6.0 ± 1.3 (2.7 to 9.9)	6.0 ± 1.3 (3.3 to 9.8)	0.194
Prefeeding nipple length (cm)	0.77 ± 0.30 (−0.10 to 1.6)	0.78 ± 0.32 (−0.10 to 1.7)	0.910
Prefeeding vertical nipple diameter (cm)	1.52 ± 0.21 (1.0 to 2.2)	1.55 ± 0.24 (1.0 to 2.4)	0.240
Prefeeding horizontal nipple diameter (cm)	1.58 ± 0.21 (0.9 to 2.2)	1.54 ± 0.21 (1.0 to 2.2)	0.213
Postfeeding nipple length (cm)^a	0.97 ± 0.27 (0.15 to 1.80)	1.01 ± 0.28 (0.20 to 1.70)	0.004
Postfeeding vertical nipple diameter (cm)	1.57 ± 0.23 (1.00 to 2.50)	1.58 ± 0.20 (0.90 to 2.60)	0.296
Postfeeding horizontal nipple diameter (cm)^a	1.54 ± 0.21 (1.00 to 2.20)	1.59 ± 0.22 (1.00 to 2.50)	0.001

Statistically significant changes between sides.

As shown in Table 3, measurements of the areola and the nipple obtained from one side correlated significantly with those of the other side. There were significant differences between the pre- and postfeeding values in terms of nipple length, but not in terms of nipple diameter (both vertical and horizontal) (means, SDs, and ranges shown in Table 2). There was a significant correlation between pre- and postfeeding nipple lengths on both sides, as shown in Figure 1.

FIG. 1.

Correlation between prefeeding nipple length (y-axis, cm) and postfeeding nipple length (x-axis, cm) on the left side (left panel) and on the right side (right panel).

Table 3.

Correlation Coefficients (R²) of Areolar and Nipple Measurements of the Left Side Versus the Right Side

	R ²	p
Prefeeding nipple length	0.65	<0.001
Postfeeding nipple length	0.50	<0.001
Nipple vertical diameter	0.39	<0.001
Nipple horizontal diameter	0.51	<0.001
Areolar vertical diameter	0.80	<0.001
Areolar horizontal diameter	0.78	<0.001

Table 4 depicts the correlation coefficients and p-value of the regression between the prefeeding nipple length (right and left side) and selected variables. Both right and left nipple length correlated weakly, but significantly, with maternal age, gravidity, parity, the number of previously breastfed infants, and the cumulative number of BF months. When analyses were limited to the 42 primiparous women of our population, prefeeding nipple length correlated significantly with maternal age both on the right side (R² = 13.7%, p = 0.016) and the left side (R² = 11.3%, p = 0.029).

Table 4.

Correlation Coefficients and p-Value of the Regression Between the Prefeeding Nipple Length (Right and Left Side) and Selected Variables

Variable	Right nipple length		Left nipple length
Variable	R² (%)	p	R² (%)	p
Maternal age (years)	4.4	0.003	7.1	<0.001
Gravidity	5.3	0.001	6.1	<0.001
Parity	6.5	<0.001	9.1	<0.001
Previous infants breastfed/woman	6.2	<0.001	7.5	<0.001
Cumulative months of BF	4.0	0.004	4.5	0.003
Early (<2 hours) placement at the breast	1.5	0.08	0.5	0.321
GA (weeks)	0.2	0.523	1.4	0.095
Areolar vertical diameter (right)	2.4	0.028	0.5	0.338
Areolar vertical diameter (left)	3.1	0.013	1.6	0.076
Areolar horizontal diameter (right)	1.7	0.063	1.2	0.129
Areolar horizontal diameter (left)	3.0	0.014	1.6	0.075
Postfeeding nipple length (right)	56.7	<0.001	NA	NA
Postfeeding nipple length (left)	NA	NA	45	<0.001

We used stepwise regression analysis, where the prefeeding nipple length (right or left) was used as the dependent variable, and parity (or maternal age, gravidity, or previous BF experience), early (<2 hours) first BF, and GA were used as the independent variables. In all analyses, GA remained insignificant, while early (<2 hours) first BF had a p-value of 0.09–0.10, and parity, maternal age, gravidity, or previous BF experience was significantly associated with nipple length (p < 0.001). Because parity, maternal age, gravidity, and previous BF experience were strongly inter-related, it was not possible to use these variables simultaneously on the same side (independent variables) of the stepwise regression analysis equation, without increasing the risk of unstable prediction equation due to colinearity.

We thus ran a stepwise regression analysis after excluding all multigravidas, using prefeeding nipple length (right or left) as the dependent variable, and maternal age and GA as the independent variables. Once again in this analysis of primiparas alone, GA remained insignificant, while maternal age was strongly associated with nipple length (R² = 17%, p < 0.001).

Discussion

In this study, we provide the basis for normal values of nipple and areolas on day 2 of BF. These values may provide lactation consultants and practitioners involved with BF with a statistical definition (mean ±2 SD) of what a “normal nipple” is, and what a flat or elongated or large nipple is; this could potentially help conducting studies on whether significant deviations from these norms are clinically significant or not in terms of BF. Importantly, our work demonstrates that the timing of these measurements in relation to BF is important, as immediately after BF, the nipple length is significantly higher than just before it, while its diameter is essentially not affected by BF.

Increasing parity, maternal age, or previous BF experience was significantly associated with increased nipple length. Since the correlation between maternal age and nipple length remained significant even in the subgroup of primiparas (which neutralizes both parity and previous BF experience), we understand from that correlation that nipples continue to “grow” overtime even after puberty in women of childbearing age. Whether or not this “growth” confers a BF advantage to older mothers remains to be proven. Indeed, in a study from Thailand, increased nipple length was reported to improves the odds of successful BF,⁶ while in a study from California, the combination of wider and longer nipples was associated with a greater risk for difficulties with latch.⁷

An interesting finding of this study was the statistically significant elongation of the postfeeding left nipple in this predominantly right-handed population. Although handedness was not found to affect nipple or areola measurements, we can only as whether these side differences could this possibly have a relationship with the comfort or ease of positioning on a specific breast, depending upon handedness. The finding that nipple length increases with age even among primiparous women is also noteworthy. Older primiparous mothers tend to have more comorbid conditions that may be associated with lactation failure. The finding that nipple length correlates positively with maternal age may provide a small counterbalance to the many risk factors associated with advancing age at first births.

A limitation to our study is that it was a cross-sectional one and we did not study longitudinally dimensional changes of the nipples. However, in view of the relatively large number of the population studied, we do not believe that nipple changes associated with advancing maternal age were due to chance alone.

Another limitation of this study is that it was conducted exclusively in a population of Jewish Caucasians, and may not be applicable to other ethnic groups. Indeed, theoretically, nipple dimensions may vary similar to breast size, known to have significant ethnic variations.⁸ Thus, the norms that we describe here might not be universal although our pre-BF nipple length data were similar to the data published in the Thai study,⁶ as well as data published by us in this journal in a different population on BMI and breast anatomy.⁹ Also, it is not clear whether, as the lactation duration increases, there are additional changes in nipple and areola dimensions over time.

An additional limitation of this study is that a single individual performed all the measurements, with the potential of introducing a systematic bias. However, this individual underwent strict training from an experienced dysmorphologist (P.M.), and this limitation might actually be a strength, as it eliminates interobserver variance, and only leaves room to intraobserver variation.

In conclusion, we here offer a set of standards that describe nipple dimensions in very early lactation, on day 2 of life. Interestingly, we found that nipple length increases with maternal age. Whether or not previous BF experience or exposure to the hormonal environment of previous pregnancies also has an additional effect upon nipple length remains to be demonstrated. The data are important for medical staff consulting mothers in early BF, and provide them with a tool that may allow reassurance about normal values of the areola and nipple. Lactating persons with either self-identified or clinician-identified “short” or “flat” nipples may have decreased BF self-efficacy.

Providing clinicians with at least a first step toward objective measurements in this may help appropriately identify those who are at the lower end of the observed mean and provide them with increased BF support. Conversely, it could also provide those with nipple lengths in the normal range reassurance of this measurement.

Footnotes

Disclosure Statement

No competing financial interests exist.

Funding Information

No funding was received for this study.

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