Aumento ponderale in gravidanza

L’aumento ponderale in gravidanza (GWG, Gestational Weight Gain) così come l’alimentazione e lo stato nutrizionale prima e durante la gravidanza influenzano profondamente il decorso della gravidanza e la salute della gravida e del feto (1-5). L’aumento ponderale in gravidanza infatti,  non  solo determina l’entità della crescita fetale  ma modula addirittura il rischio di malformazioni fetali (gastroschisi e labiopalatoschisi in particolare), malattie e mortalità del feto. Questo rapporto  non si limita al solo periodo gestazionale o neonatale, ma si estende anche alla fanciullezza e all’età adulta (6-8). Ad esempio, i feti IUGR (“Intra Uterine Growth Restriction”), così come i bambini  denutriti, si adattano a tali condizioni avverse tramite modificazioni dell’apparato cardiovascolare (stenosi arteriose) e del  metabolismo (insulino-resistenza e diabete) e tali particolari modificazioni tendono a persistere per tutta la vita (9,10).

Prendendo in considerazione i recenti dati demografici della donna fertile, l’Organizzazione Mondiale della Sanità (World Health Organization’s, WHO)  ha presentato nuove linee guida (67) per la valutazione del GWG utilizzando come parametro base l’indice di massa corporea (Body Mass Index, BMI), valore ottenuto dividendo il numero di Kg del peso per l’altezza in metri elevata al quadrato, Kg/m²) (11).  Le gravide sono state classificate e suddivise in base al BMI  pre-gravidico e per ogni gruppo è stato calcolato il GWG ideale (12-15). Per le donne che hanno un peso normale prima della gravidanza con BMI di 18,5-24,9 l’aumento di peso dovrebbe essere di 13-20 Kg. Le donne sottopeso prima  dell’inizio di gravidanza con un BMI <18,5 dovrebbero aumentare di 15-25 Kg. Le donne che ad inizio di gravidanza sono in sovrappeso, con un BMI di 25-29, dovrebbero guadagnare non oltre i 12 Kg. Le donne con grave obesità pre-gravidanza, BMI ≥30, dovrebbero cercare di contenere  l’aumento ponderale entro i 10-11 Kg. Un incremento ponderale maggiorato del 10-20% rispetto a quanto raccomandato è consentito  alle gravidanze gemellari, alle adolescenti, alle primipare ed alle gravide che svolgono un’intensa attività fisica (16).

Aumento ponderale medio in gravidanza:

• Primo trimestre: 1-2 Kg
• Secondo trimestre: 1 Kg a settimana
• Terzo trimestre: 0.5-1 Kg a settimana

Distribuzione percentuale media dell’aumento di peso in gravidanza: Il peso mediamente acquisito da una gravida a termine, normopeso pre-gravidica,  dovrebbe essere  di 14.3 Kg, così suddiviso:

A)  6 Kg:  feto, liquido amniotico e placenta
B)  8.3 Kg: utero, liquidi extracellulari, plasma, sangue e tessuto adiposo.

E precisamente:

• 3.400 gr il peso del feto a termine
• 2.000 gr grasso sottocutaneo
• 2.500 gr aumento  del volume plasmatico
• 2.500 gr aumento del liquido extra-cellulare
• 600 gr aumento del volume del sangue.
• 800 gr  aumento di peso del tessuto mammario.
•  900 gr liquido amniotico
• 800 gr  placenta
• 800 gr  utero

per un totale, in media, di 14.3  Kg a termine di gravidanza.

MANCATO o RIDOTTO INCREMENTO PONDERALE

Le cause di mancato incremento ponderale in gravidanza sono:

1. quasi esclusivamente da attribuire ad uno scarso apporto calorico: dieta <1800 KCal/die. Le restrizioni alimentari sono una causa dello scarso incremento ponderale materno in gravidanza e si associano ad anemia e depressione postpartum. Inoltre si associano ad iperemesi gravidica che a volte è espressione di una bulimia latente e sembra correlarsi ad una maggiore incidenza di labiopalatoschisi (17-19).
2. IUGR
3. L’abitudine al fumo: In gravidanza il fumo di sigaretta può interferire con la normale crescita ed il corretto sviluppo del feto. La nicotina ed il monossido di carbonio infatti interagiscono con l’ossigenazione fetale e ne limitano lo sviluppo. Meglio quindi non fumare ed in ogni caso non superare le 5 sigarette al giorno. Il fumo aumenta in modo significativo il rischio di aborto, parto prematuro e ridotto sviluppo del feto.
4.  adolescenti: Le adolescenti gravide hanno un rischio particolarmente aumentato di avere un basso peso pregravidico e uno scarso incremento di peso in gravidanza. Esse inoltre possono presentare con maggior frequenza: anemia, infezioni e complicanze ostetriche conseguenti anche ad un eventuale basso livello economico-culturale (19).
5. età avanzata 
6. caffè: la caffeina è in grado di attraversare la placenta. Un eccesso di caffeina in gravidanza induce scarso aumento ponderale e può portare aborti spontanei e basso peso neonatale (SGA, Small for Gestational Age). Il caffè tostato contiene alte percentuali di ferro (96,97).
   
7. malassorbimento intestinale
8. celiachia
9. iperemesi
10. sport agonistico
11. tireopatie
12. diabete mellitoridotto aumento ponderale in gravidanza:
13. basso livello socio-economico e culturale
14. patologie cardiache
15. uso di farmaci

Complicanze da ridotto incremento ponderale in gravidanza: Il mancato aumento ponderale in gravidanza comporta un maggior rischio di patologie ostetriche e condiziona particolari esigenze nutrizionali, come ad esempio un maggior fabbisogno di cibi contenenti sostanze antiossidanti naturali. Conseguenze di scarso aumento ponderale nel I° trimestre sono costituite anche da un’aumentata percentuali di malformazioni fetali ed aumentato rischio di minaccia di aborto, aborto e morte improvvisa fetale. Nel II° e III° trimestre inevitabilmente il feto va incontro ad episodi di ipossia e a  rallentato accrescimento intrauterino (IUGR) e basso peso alla nascita in rapporto all’epoca gestazionale (15). Il peso del feto è direttamente correlato al BMI materno pregravidico, ma anche all’incremento di peso materno in gravidanza, oltre che al potenziale di crescita del feto, determinato geneticamente, e alla funzionalità della placenta. Uno studio effettuato dall’Organizzazione Mondiale della Sanità su 110.000 nati in 20 Paesi ha confermato che il ridotto peso neonatale ha come cause principali il basso peso materno prima della gravidanza, che aumenta il rischio di 2.38 volte, ed il lieve incremento di peso alla 36^a settimana di gestazione, che lo incrementa di 2.59 volte. L’iponutrizione e/o l’ipossia durante determinati periodi critici della vita intrauterina possono causare alterazione della “programmazione” della struttura e funzione cardiovascolare e metabolica. Si verifica nel feto, in caso di ritardo di crescita, una vasocostrizione di tutti i vasi sanguigni periferici che orienta preferenzialmente il flusso ematico verso gli organi vitali nobili (cervello e cuore), con finalità di compenso e protezione (centralizzazione del circolo), ma talora con conseguenze non del tutto reversibili sulla distensibilità delle grandi arterie. Il basso peso fetale aumenta il rischio di sviluppare da adulto insulino resistenza, ovvero resistenza all’effetto dell’insulina, o diabete non insulino dipendente, detto anche dell’adulto o di tipo 2, ed obesità centrale, ovvero disposta prevalentemente nell’addome (14-16).

ECCESSIVO INCREMENTO PONDERALE IN GRAVIDANZA (EGWG):

Cause di un eccessivo GWG:

• Obesità pre-gravidica (BMI >29): è notevolmente aumentata negli ultimi 20 anni (20)
• Fattori costituzionali, familiari e culturali (21,22)
• elevata concentrazione plasmatica di leptina (23-26)
• dieta ipercalorica (>2800 KCal/die): nella errata convinzione popolare che in gravidanza occorre mangiare “per due”, le gravide soprattutto giovani (27), di estrazione popolare (26) e alla prima gravidanza sono invogliate da parenti ed amici a mangiare di tutto e di a più (28-31).
• stress (fame da stress) e insonnia (29-33)
• Astinenza dal fumo: La nicotina aumenta il metabolismo basale, aiutando a bruciare più calorie. Fumare fa anche diminuire l’appetito e altera il senso del gusto, facendo sembrare meno buoni i cibi che mangiamo. C’è soprattutto un fattore psicologico che interviene quando si rinuncia alla sigaretta: si sente il desiderio di doverla sostituire in qualche modo. In questo  il cibo si rivela il sostituto più ricercato, soprattutto cioccolato, patatine e caramelle.
• Vita sedentaria: Secondo i dati del Censis 2013, il 40% degli Italiani sono teledipendenti da bambini e sedentari da adulti. Se a ciò si aggiunge l’abbandono delle normali attività lavorative in gravidanza, il metabolismo ne risente con aumento di peso (22). Infatti, l’attività fisica e lo sport, non  bruciano solo calorie ma anche i grassi e  anche a riposo, dopo lo sport.

Le conseguenze dell’eccessivo incremento ponderale sono costituite principalmente da alterazioni metaboliche materno-fetali a breve e lungo termine (40-48) e aumentata incidenza di malformazioni fetali (48,49):

• aumentato rischio di taglio cesareo (35-37)
• intolleranza al glucosio e diabete gestazionale (38-40)
• Mancata riduzione del peso post-partum e/o obesità (BMI >25) post-partum  con aumentato rischio di varicosità e  trombosi venosa profonda (41-49)
• fallimento dell’allattamento al seno o ridotto periodo di allattamento al seno. Lo stesso rischio è presente in caso di ridotto GWG (50-60). Le cause sono molteplici: difficoltà a posizionare correttamente il lattante durante l’allattamento per l’eccessiva grassezza e la ridotta sintesi di prolattina post-partum sia basale che durante lo stimolo della suzione (59).
• gestosi ipertensiva (61,62)
• patologie cardio-vascolari (63)
• parto prematuro (64-69)
• Aumentato rischio di lacerazioni durante il parto (70)
• macrosomia fetale: La macrosomia fetale ha come conseguenze la maggiore durata del travaglio, il rischio di parto cesareo (35-37), di distocia di spalla, ipossia fetale (35-37,71-73), morte fetale intrauterina (74-82); le percentuali di macrosomia fetale sono decisamente aumentate negli ultimi decenni e conseguentemente  il diabete infantile, obesità neonatale, sindrome metabolica, asma e cancro (83-87).
• obesità neonatale ed in età adulta:  ogni chilogrammo acquisito dalla madre porta a un aumento di 7,35 grammi nel peso del figlio (83-87).
• Alterazioni del tubo neurale fetale (88,89)
• Predisposizione a fenomeni flogistici, in particolare dell’apparato odontostomatologico (90)

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