You will be presented with the full text of a biomedical research paper. Please write an abstract for this paper. Your response should include the abstract and no additional text.

Paper text:
routine symphysis - fundal height ( or  fundal height  in short ) measurement during pregnancy has been used in antenatal care with a long history , to estimate size of uterus and gestational age .
. abnormal fundal height ( smaller or larger than gestational age ) may indicate abnormal uterus , fetal growth , and amniotic fluid development .
fundus smaller than gestational age may indicate intrauterine growth restriction ( iugr ) , small for gestational age ( sga ) , or oligohydramnios , while fundus larger than gestational age may reflect large fetus for gestational age ( lga ) , polyhydramnios , twins , or uterine tumor . although ultrasound is replacing fundal height measurement in detecting the above conditions [ 6 , 7 ] , in developing countries , it is not fully available in all antenatal care levels , due to high cost and lack of experienced personnel [ 1 , 3 ] . therefore who reproductive health library still recommends using fundal height measurement as a tool to estimate gestational age and detect sga and multiple pregnancies .
national institute for health and clinical excellence guideline for antenatal care ( clinical guideline 62 ) also recommends routine measurement and monitoring fundal height for every antenatal visit . according to cochrane review
, there is not enough evidence to evaluate the use of fundal height measurement during antenatal care ; on the other hand , there is also insufficient evidence to determine whether fundal height measurement is not effective .
the sensitivity of fundal height measurement in detecting iugr , sga , and lga varies from 17% to 86% [ 10 , 11 ] , due to differences in gestational age assessment and fundal height measurement techniques .
many studies therefore recommend demographically specific fundal height growth curve rather than universally derived curve , as fundal height is influenced by ethnicity , socioeconomics , and nutritional status [ 1215 ] .
fundal height growth curves in thai women were derived from specific setting with different subject selection and gestational age assessment [ 16 , 17 ] .
most settings were university hospitals located in bangkok , while the majority of pregnant women attended the general hospitals or primary care settings and most of them were from middle to low economic status .
gestational age assessment by last menstrual period ( lmp ) in the past   was replaced by ultrasound in more recent studies .
although ultrasound is more accurate during the first half of pregnancy , both methods are still applied in most antenatal care services .
we developed fundal height growth curve from normal singleton pregnancy in general hospitals , using gestational age assessment both from lmp and/or ultrasound to reflect routine antenatal care practice .
the derived fundal height growth curve is expected to be used in the northern part of thailand .
all data were obtained from thai women who attended antenatal care and delivered at four university affiliated hospitals in the upper northern part of thailand , two provincial hospitals and two regional hospitals , between january 2009 and march 2011 .
being administered under the ministry of public health of thailand , the four hospitals have a similar guideline for antenatal care practice .
subject eligible criteria were normal singleton pregnant women who started antenatal care before 20 weeks of gestation .
pregnant women with uncertain gestational age and medical or obstetrical complications affecting fetal growth and those with habitual smoking , alcohol drinking , and drug abuse during pregnancy were excluded from the study .
gestational age was calculated from ( 1 ) first day of lmp if regular menstruation and correlated with size of uterus by palpation or correlated with gestational age by ultrasound ( not more than 1 week difference ) or ( 2 ) ultrasound in the first half of pregnancy if lmp uncontained or size of uterus not correlated with lmp or gestational age by lmp not correlated with ultrasound ( more than 1 week difference ) .
fundal height was measured in centimeters with nonelastic measurement tape from the upper border of the symphysis pubis to the top of the uterine fundus , or reversed direction .
all measurements were performed by or under supervision of registered nurses or obstetricians who had at least 2 years of experience with obstetric prenatal care , in order to minimize measurement error and bias .
fundal height and gestational age were recorded from the beginning to the end of antenatal care .
assessment of gestational age and measurement of fundal height were standardized by a correction factor calculated from systematic error by a regression technique .
a second - degree polynomial equation was fitted using a multilevel model for continuous data .
a quadratic regression model was used to predict the 10th , 50th , and 90th percentiles of fundal height .
the fundal height growth curve was presented as smoothed function of the 10th , 50th , and 90th percentiles between 20 and 40 weeks of gestation .
the study protocol was approved by the research ethics committee , faculty of medicine , chiang mai university , and the research ethics committee of the four hospitals .
during the study period , there were 2,351 pregnant women who attended antenatal care and delivered at the four hospitals .
696 ( 67.0% ) were from provincial hospitals and 342 ( 33.0% ) from regional hospitals .
the average age was 25.6 years ( sd = 6.2 ) , body mass index ( bmi ) was 21.6  kg / m ( sd = 3.8 ) , and gestational age at first antenatal visit was 13 weeks ( sd = 5.0 ) .
the average of total pregnancy weight gain was 13.5  kg ( sd = 4.7 ) , gestational age at delivery was 39.2 weeks ( sd = 1.1 ) , and birth weight was 3,120.3  g ( sd = 325.0 ) ( table 1 ) .
gestational age was calculated from lmp in 648 women ( 62.4% ) and from ultrasound in 390 women ( 37.6% ) .
ultrasound was done at the average gestational age of 16 weeks ( sd = 5.2 ) .
a total of 7,634 fundal height ( fh ) measurements were used with 111 missing data ( 1.4% ) .
the remaining 7,523 measurements ( 98.6% ) were analyzed , averaged 7.3 measurements per woman ( sd = 2.1 ) and 358.2 measurements per week ( range : 119840 ) .
the fundal height was likely to be equally distributed across each gestational age ( ga ) with an obvious monotonous increment from 19.1  cm ( sd = 1.9 ) at 20 weeks to 35.4  cm ( sd = 2.4 ) at 40 weeks ( table 2 and figure 1 ) .
the maximum increase of 1.0  cm / wk was observed between 20 and 32 weeks , declining to 0.7  cm / wk between 33 and 36 weeks and 0.3  cm / wk between 37 and 40 weeks ( table 2 ) . the fundal height obtained from quadratic regression equation allowing for random ( individual ) effect ; 
 ( 1)fh  ( cm)=19.7882 + 2.438157  ga  ( wk)0.0262178  ga2  ( wk ) .
the above equation explained 85% of the variation ( r - squared = 0.85 ) .
the final fundal height growth curve ( figure 2 ) was presented as smoothed function of the 10th , 50th , and 90th percentiles derived from table 3 .
our fundal height growth curve was different from previous studies ( table 4 ) in the aspect of week - specific value , slope , and curve pattern [ 1220 ] .
these could be due to differences in ethnicity , socioeconomic , life style , nutritional status , study methodology , eligible criteria , gestational age definition , fundal height measurement , and statistical analysis .
our growth curve has a quadratic pattern similar to studies in thailand [ 16 , 17 ] , tanzania , and nigeria   but was different from studies in sweden   and mozambique   which had cubic pattern curves .
thai women are relatively smaller and have relatively smaller pelvis compared to caucasian women , causing an increase in a fundal height early in pregnancy ( figure 2 ) .
enlargement of fundal height in caucasian women with relatively larger and broader pelvis   was noticeable later in pregnancy , causing an s - shaped ( cubic curve ) .
black women with african ethnicity with anthropoid typed pelvis ( long anteroposterior diameter , short transverse diameter )   had similar fundal height pattern of growth curve to thai women but did not decline around term due to unengagement .
an exception was observed in some african ethnic with gynecoid pelvis . confined to fundal height growth curve in thai women ,
our curve is 1.0  cm above the study in 1984 , but 0.5 to 1.0  cm below the study in 2001   ( figure 3 )
. the discrepancies may reflect difference population and/or study methodology , including the cohort effect . the fact that mean
birth weight in the northern part of the country increased from 2,933  g in 1982   to 3,117  g in 2011   may explain the latter hypothesis .
it is worth noticing that gestational age in three studies used different criteria ( figure 3 ) .
although gestational age by lmp tends to overestimate ultrasound [ 28 , 29 ] , our study had explored and confirmed that gestational age by lmp and by ultrasound was very close .
errors in ultrasound are less in women with low bmi . the fact that our subjects had an average bmi 21.6  kg / m ( sd = 3.8 )
may explain the above statement . as mentioned above , it is therefore essential that each population should have its own fundal height growth curve to use in screening for abnormal intrauterine growth .
event in the same country , different context of ethnicity , and socioeconomic , measurement method also lead to difference in fundal height growth curve .
our study focuses on development of fundal height growth curve based on routine antenatal care practice in the northern part of thailand , which may be different from the rest of the country .
the regression technique in our study considered correlation of fundal height and gestational age within the same subject .
a multilevel model for continuous data using longitudinally collected data is more appropriate than a cross - sectionally collected data in some studies .
observable larger variation of fundal height early and late pregnancy ( figure 1 ) may be obscured by thick abdominal wall especially in early pregnancy and fetal engagement beyond 37 weeks .
existing fundal height growth curve used difference criteria : lower - upper limit , 1 to 2 standard deviation , and the 10th to 90th percentile or 5th to 95th percentile .
we also recommend monitoring fundal height at every antenatal visit . medical consultation or further investigation
is recommended when fundal height is below the 10th , or above 90th percentile ; fundal height growth rate decelerates , stabilizes or declines , or increases rapidly .  
screening for abnormal uterine growth and gestational age in the past assumed a constant linear equation ; fh ( cm ) = ga ( wk ) 2 , for pregnancy 2036 weeks . there was a strong statistical evidence that our data fitted more appropriately with a quadratic pattern ( p < 0.001 from likelihood - ratio test ) .
however , one should be aware that fundal height measurement is more or less subjective to error , either from intra- or interobservers .
being a retrospective data collection , some of the data were inevitably incomplete . our study , however , tried to collect a large sample sized data to allow for missing values .
like other clinical prediction rules , the derived fundal height growth curve should be validated before putting into routine clinical practice .
a demographically specific fundal height growth curve is a simple tool for monitoring intrauterine growth and screening for abnormal uterine growth . applying fundal height growth curve into routine antenatal care practice
may reduce unnecessary ultrasound in fully equipped settings and reduce unnecessary referring for further investigations in resource - deprived settings .
objectives . to develop fundal height ( fh ) growth curve from normal singleton pregnancy based on last menstrual period ( lmp ) and/or ultrasound dating for women in the northern part of thailand . 
 methods . 
 a retrospective time - series study was conducted at four hospitals in the upper northern part of thailand between january 2009 and march 2011 . 
 fh from 20 to 40 weeks was measured in centimeters . 
 the fh growth curve was presented as smoothed function of the 10th , 50th , and 90th percentiles , which were derived from a regression model fitted by a multilevel model for continuous data . 
 results . 
 fh growth curve was derived from 7,523 measurements of 1,038 women . 
 gestational age was calculated from lmp in 648 women and ultrasound in 390 women . 
 the fh increased from 19.1  cm at 20 weeks to 35.4  cm at 40 weeks . 
 the maximum increase of 1.0  cm / wk was observed between 20 and 32 weeks , declining to 0.7  cm / wk between 33 and 36 weeks and 0.3  cm / wk between 37 and 40 weeks . 
 a quadratic regression equation was fh ( cm ) = 19.7882 + 2.438157  ga  ( wk )  0.0262178 ga2 ( wk ) ( r - squared  =  0.85 ) . 
 conclusions . 
 a demographically specific fh growth curve may be an appropriate tool for monitoring and screening abnormal intrauterine growth .