Late pregnancy: impact on prematurity and newborn’s weight

Shimamura, Lia Keiko Sousa; Monteiro, Denise Leite Maia; Silva, Célia Regina da; Morgado, Flávio Eduardo Frony; Souza, Flávio Monteiro de; Rodrigues, Nádia Cristina Pinheiro

doi:10.1590/1806-9282.20210454

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Revista da Associação Médica Brasileira

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Original Article • Rev. Assoc. Med. Bras. 67 (11) • Nov 2021 • https://doi.org/10.1590/1806-9282.20210454 copy

Late pregnancy: impact on prematurity and newborn’s weight

Authorship SCIMAGO INSTITUTIONS RANKINGS

SUMMARY

OBJECTIVE:

This study aimed to evaluate the frequency of late pregnancies in Brazil, the age-specific fertility rate (ASFR) in the regions, the rate of prematurity, and the rate of low birth weight (LBW) and their association with advanced maternal age compared with 20–34-year-old women.

METHODS:

This was a cross-sectional study conducted by searching the Information System on Live Births (Sistema de Informações Sobre Nascidos Vivos [SINASC]). Data from 1995 to 2018 were collected, and pregnant women were divided into three categories based on their age range: 35–39, 40–44, and ≥45 years. The study calculated the frequency of deliveries of mothers of advanced age in Brazil, the ASFR, and the rates of prematurity and LBW in each group.

RESULTS:

The frequency of newborns (NB) of mothers aged ≥35 years increased by 64%. The 35–39-year-old ASFR increased in all regions, except in the northeast. At maternal age ≥35 years, NB increased by 58% between 28 and 36 weeks during the study period. LBW increased between 500 and 1,499 g in 68.7% and between 1,500 and 2499 g in 57% of cases. In 2018, regarding the age range of 20–34 years, the chance of premature delivery was 29% at 35–39 years (OR=1.29), 54% higher at 40–44 years (OR=1.54), and 114% higher at ≥45 years (OR=2.14); while the chance of LBW increased by 28% at 35–39 years (OR=1.28), 56% at 40–44 years (OR=1.56), and 139% at 45 years or older (OR=2.39).

CONCLUSIONS:

The frequency of deliveries and ASFR ≥35 years increased between 1995 and 2018. The chances of prematurity and LBW were higher with increased maternal age.

KEYWORDS:
Prematurity; Maternal age; Fertility rate; Pregnancy complications; Low birth weight

North region
Maternal age (years)	1995–2000			2001–2006			2007–2012			2013–2018			Variation 2013–2018 to 1995–2000
Maternal age (years)	Fem. pop.	N° LB	ASFR/1,000	Fem. pop.	N° LB	ASFR/1,000	Fem. pop.	N° LB	ASFR/1,000	Fem. pop.	N° LB	ASFR/1,000	Variation 2013–2018 to 1995–2000
35–39	2,019,196	64,013	31.7	2,512,602	79,561	31.7	3,119,241	97,624	31.3	3,984,599	132,498	33.3	4.9%
40–44	1,590,054	1,9250	12.1	2,040,078	22,423	11.0	2,626,489	25,694	9.8	3,312,505	32,224	9.7	-19.6%
45–49	1,212,189	2,293	1.9	1,742,507	2,608	1.5	2,194,995	2,471	1.1	2,680,054	2,375	0.9	-53.2%
Total	8,612,299	85,556	9.9	10,555,205	104,592	9.9	14,082,620	125,789	8.9	9,977,158	167,097	16.7	68.6%
Northeast region
Maternal age (years)	1995–2000			2001–2006			2007–2012			2013–2018			Variation 2013–2018 to 1995–2000
Maternal age (years)	Fem. pop.	N° LB	ASFR/1,000	Fem. pop.	N° LB	ASFR/1,000	Fem. pop.	N° LB	ASFR/1,000	Fem. pop.	N° LB	ASFR/1,000	Variation 2013–2018 to 1995–2000
35–39	8,407,568	290,313	34.5	9,863,931	329,563	33.4	11,048,258	345,828	31.3	13,234,508	441,184	33.3	-3.5%
40–44	7,043,303	92,026	13.1	8,162,943	98,462	12.1	10,206,393	95,591	9.4	11,529,569	107,354	9.3	-28.7%
45–49	26,515,402	11,463	0.4	30,959,251	9,120	0.3	39,417,304	7,820	0.2	24,764,077	7,106	0.3	-33.6%
Total	42,247,527	394,329	9.3	48,986,125	437,374	8.9	60,671,955	449,822	7.4	49,528,154	556,289	11.2	20.3%
Central-west region
Maternal age (years)	1995–2000			2001–2006			2007–2012			2013–2018			Variation 2013–2018 to 1995–2000
Maternal age (years)	Fem. pop.	N° LB	ASFR/1,000	Fem. pop.	N° LB	ASFR/1.000	Fem. pop.	N° LB	ASFR/1.000	Fem. pop.	N° LB	ASFR/1,.000	Variation 2013–2018 to 1995–2000
35–39	2,333,033	57,883	24.8	2,880,175	72,237	25.1	3,335,263	95,671	28.7	3,934,303	145,312	36.9	48.9%
40–44	1,880,647	12,956	6.9	2,344,215	15,807	6.7	3,007,460	21,139	7.0	3,486,192	31,722	9.1	32.1%
45–49	1,444,370	1,167	0.8	2,047,978	990	0.5	2,611,653	1,304	0.5	3,075,702	1,823	0.6	-26.6%
Total	9,589,369	72,006	7.5	12,061,893	89,034	7.4	16,313,916	118,114	7.2	10,496,197	178,857	17.0	126.9%
Southeast region
Maternal age (years)	1995–2000			2001–2006			2007–2012			2013–2018			Variation 2013–2018 to 1995–2000
Maternal age (years)	Fem. pop.	N° LB	ASFR/1.000	Fem. pop.	N° LB	ASFR/1.000	Fem. pop.	N° LB	ASFR/1,000	Fem. pop.	N° LB	ASFR/1,000	Variation 2013–2018 to 1995–2000
35–39	16,060,684	527,001	32.8	18,278,641	590,144	32.3	18,539,827	660,988	35.7	21,046,815	875,035	41.6	26.7%
40–44	13,754,946	123,286	9.0	16,264,584	146,153	9.0	17,807,649	164,219	9.2	19,052,960	205,111	10.8	20.1%
45–49	10,986,161	8,886	0.8	14,665,077	8,632	0.6	16,744,024	9,623	0.6	17,542,724	11,814	0.7	-16.7%
Total	76,884,903	659,173	8.6	91,095,225	744,929	8.2	111,158,805	834,830	7.5	57,642,499	1,091,960	18.9	121.0%
South region
Maternal age (years)	1995–2000			2001–2006			2007–2012			2013–2018			Variation 2013–2018 to 1995–2000
Maternal age (years)	Fem. pop.	N° LB	ASFR/1,000	Fem. pop.	N° LB	ASFR/1,000	Fem. pop.	N° LB	ASFR/1,000	Fem. pop.	N° LB	ASFR/1,000	Variation 2013–2018 to 1995–2000
35–39	5,519,462	223,716	40.5	6,379,145	217,083	34.0	6,121,427	218,629	35.7	6,674,118	287,767	43.1	6.4%
40–44	4,701,741	57,822	12.3	5,526,089	58,271	10.5	6,157,495	56,852	9.2	6,220,413	67,198	10.8	-12.2%
45–49	3,806,339	4,697	1.2	5,005,921	3,735	0.7	5,867,858	3,426	0.6	6,027,612	3,652	0.6	-50.9%
Total	26,305,429	286,235	10.9	31,199,313	279,089	8.9	37,957,265	278,907	7.3	44,120,618	358,617	8.1	-25.3%
Brazil
Maternal age (years)	1995–2000			2001–2006			2007–2012			2013–2018			Variation 2013–2018 to 1995–2000
Maternal age (years)	Fem. pop.	N° LB	ASFR/1.000	Fem. pop.	N° LB	ASFR/1.000	Fem. pop.	N° LB	ASFR/1.000	Fem. pop.	N° LB	ASFR/1.000	Variation 2013–2018 to 1995–2000
35–39	34,339,943	1,162,926	33.9	39,914,494	1,288,588	32.3	42,164,016	1,418,740	33.6	48,874,343	1,881,796	38.5	13.7%
40–44	28,970,691	305,340	10.5	34,337,909	341,116	9.9	39,805,486	363,495	9.1	43,601,639	443,609	10.2	-3.5%
45–49	24,492,362	109,069	4.5	31,624,426	114,427	3.6	37,624,923	112,415	3.0	40,855,661	127,018	3.1	-30.2%
Total	87,802,996	1,577,335	18.0	105,876,829	1,744,131	16.5	119,594,425	1,894,650	15.8	133,331,643	2,452,423	18.4	2.4%

		1995–2000		2001–2006		2007–2012		2013–2018		Variation in the period 1995–2018 (%)
		Freq.	%	Freq.	%	Freq.	%	Freq.	%	Variation in the period 1995–2018 (%)
Gestational age (weeks)
	22–27	7,178	8.4	6,170	9.9	8,291	11.4	12,362	14.3	70.2
	28–36	32,828	10.0	127,307	11.5	176,266	13.1	294,299	15.8	58.0
	37–41	1,209,895	8.0	1,483,394	8.9	1,567,948	10.2	1,955,544	13.3	66.3
	≥42	40,873	7.7	17,807	8.3	21,882	7.7	43,633	8.4	9.1
	Total	1,290,774	8.1	1,634,678	9.1	1,774,387	10.4	2,305,838	13.4	65.4
NB weight (g)
	Less than 500	247	1.0	547	12.1	1,525	11.1	2,445	13.5	1,200.2
	500–1,499	8,945	10.5	22,906	12.3	27,865	14.2	36,628	17.7	68.7
	1,500–2,499	90,200	10.2	142,155	11.4	154,775	12.8	196,437	16.1	57.0
	2,500–3,999	1,069,815	7.7	1,349,170	8.7	1,633,763	11.1	1,931,823	13.0	69.3
	4,000 or more	106,274	10.9	108,288	11.5	108,812	12.5	137,914	15.7	44.3
	Total	1,275,481	8.1	1,623,066	9.1	1,926,740	11.3	2,305,247	13.4	67.2
Association between maternal age and prematurity (Brazil, 2018)
	Maternal age (years)	Freq	%	p-value	OR (95%CI)
	20–34	205,831	10.3
	35–39	46,451	12.9	<0.001	1.29 (1.27–1.30)
	40–44	12,707	15.0	<0.001	1.54 (1.51–1.57)
	>45	954	19.7	<0.001	2.14 (1.99–2.30)
Association between maternal age and low birth weight (Brazil, 2018)
	Maternal age (years)	Freq.	%	p-value	OR (95%CI)
	20–34	159,564	7.9		c
	35–39	36,004	9.8	<0.001	1.28 (1.26–1.30)
	40–44	10,076	11.7	<0.001	1.56 (1.53–1.59)
	≥45	900	18.3	<0.001	2.39 (2.23–2.57)

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[1] *Corresponding author: liakeiko@hotmail.com